Injection Molding Materials

The short answer Yes, and for packaging and automotive work it is increasingly compulsory. In-house regrind can be fed back at high ratios with little loss; post-consumer recyclate is normally blended at 10 to 35 percent and needs tighter inspection, because molecular weight, colour and odour vary by batch and impact strength can drop by a quarter or more. PIR and PCR are not the same thing The distinction matters commercially because only one of them counts towards a regulatory target. Post-industrial regrind, sometimes called PIR, is your own scrap: runners, sprues, offcuts and rejected parts that never left the factory. It is clean, single-material and well understood, and a well-run moulding shop can feed it back at a high ratio, sometimes to 100 percent on non-critical parts. Post-consumer recyclate, or PCR, comes from products that were used and then collected: bottles, crates, bumpers, appliance housings. It carries the ageing, contamination and colour history of everything it has been through. Regulations such as the European packaging rules count only PCR, explicitly excluding production scrap, which means a claim built on regrind alone does not satisfy them. Chemical recycling, where waste is depolymerised back to monomer, produces material close to virgin quality and can reach food-contact grades, but capacity is small and the cost is high. A high regrind ratio is not evidence of a circular product. Only post-consumer material counts for most regulatory targets. What the regulation now requires Recycled content has moved from a voluntary claim to a market-access condition, and the numbers are specific. Under the European packaging and packaging waste regulation, from 2030 plastic packaging components must meet minimum post-consumer recycled content averaged per production site per year: 30 percent for PET in direct food and drink contact, 10 percent for other contact-sensitive plastics, and 35 percent for all other plastic packaging. From 2040 those rise to 50, 25 and 65 percent respectively. Single-use PET drinks bottles have had a 25 percent requirement since 2025 and move to 30 percent in 2030. A separate vehicle rule requires new vehicles placed on the market from 1 January 2030 to contain at least 25 percent recycled plastic by weight, with at least 10 percent from post-consumer sources, and plastic parts above 100 grams have to carry material identification marking. Comparable instruments exist outside Europe, including a tax on plastic packaging below 30 percent recycled content in the United Kingdom and a 50 percent recycled-content requirement for plastic beverage bottles in California by 2030. The targets are phased and category-specific, and they are averaged per plant rather than per part. Where recycled feedstock loses performance Every thermal cycle the polymer has already been through leaves its mark. Chain scission during the original processing and during service shortens the molecules, and the shorter the chains, the lower the impact strength and elongation. That is why the losses are not evenly distributed across the property list. Stiffness usually survives recycling well. Impact and elongation are where the losses concentrate. Impact and elongation first. A 25 to 40 percent loss in notched impact strength is common on a heavily reprocessed engineering resin, and the part becomes brittle rather than weak. Snap fits, hinges and anything drop-tested should be re-validated, not assumed. Melt flow and process window. Melt index drifts between batches, so fill pressure, packing and shrinkage move. On a multi-cavity tool that shows up as flash or short shots that change from one lot to the next. Colour and odour. Sources have different pigment histories, so natural-colour recyclate is rarely consistent enough for a cosmetic part without a dark or heavily loaded masterbatch. Residual odour matters for interiors and consumer goods, and volatile organic compounds from PCR have to be screened for automotive interior duty. Contamination and compatibilisers. Trace amounts of other polymers, printing inks and legacy additives can act as stress concentrators, and the stabilisers already in the recyclate can interact with the additives in a new compound. Restricted substances. Material from unknown waste streams can carry substances restricted by market regulations, so incoming PCR is normally screened by X-ray fluorescence and gas chromatography rather than trusted on a certificate alone. Regrind in practice: the ratio question There is no universal safe percentage, and any supplier who quotes one without asking about the part is guessing. The sensible approach is to tie the ratio to the critical property. Clean, single-material in-house regrind with controlled particle size and a closed loop can run at high ratios on non-cosmetic industrial parts. Blending 10 to 20 percent regrind into a virgin stream is a common conservative default for engineering parts, and many programmes cap total recycled content at 25 to 30 percent where impact strength is critical. Regrind must not include mixed colours, contaminated parts, or material from a previous job in a different resin, and it must be dried again before use because the smaller, dustier fraction takes up moisture faster than virgin pellets. Keep regrind out of flow lines and gate areas where weld-line strength matters, and re-validate the first article whenever the ratio changes. Design rules that make recycled content work Raise the wall, not the load. Design for uniform wall thickness and generous radii. Recycled grades tolerate stress concentrations badly, so thicker sections, larger fillets and ribs at 50 to 60 percent of the nominal wall buy more than a higher grade of recyclate. Specify colour generously. Assume the natural colour will vary. Design for a dark or opaque masterbatch load that swamps batch variation rather than a tight colour match. Keep the material mono. One polymer family per part, no incompatible overmoulds where the part has to be recycled again, and no adhesives or inserts that cannot be separated. Set the approval on a real sample. Ask for a first article on the actual recyclate lot, with impact and dimensional results, rather than on a certificate. Increase the safety factors. Where a virgin part was designed at a 2:1 factor, a recycled part may need more, because the property you are relying on is the one that degrades first. Document the chain. Recycled-content claims are audited. Keep the mass balance, the supplier certificate and the incoming inspection records with the part history. The limits: when recycled is the wrong answer Food contact is a grade question, not a percentage question. Contact-sensitive applications have both a recycled-content obligation and a migration limit. Not all recyclate streams are permitted for direct contact, and the permitted route is usually chemical recycling or an approved food-grade PCR grade. Safety-critical and high-cycle parts. Where a part protects a person or fails in a dangerous way, the variability of recyclate is a poor fit unless the design has been re-validated with margin. Optics and transparency. Clear recyclate is scarce, contamination shows immediately, and the haze level usually rules it out for lenses and light guides. Thin-wall and long-flow parts. Recyclate often has a lower and less consistent melt index, which makes a thin wall or a long flow path a filling risk. Availability is not guaranteed. PCR supply is driven by collection and sorting, so a grade can be unavailable in one quarter and plentiful in the next. Programs locked to a single recyclate source carry a supply risk that a virgin resin does not. Certification has to be real. A recycled-content claim needs third-party evidence, normally a certification such as RecyClass, ISCC PLUS or EuCertPlast to the EN 15343 standard, plus a mass balance. Marketing language without that paperwork does not survive an audit. How to specify recycled content and get it verified Tell us the regulatory target you have to meet and by when, whether the recycled content has to be post-consumer or can include your own regrind, the critical property - usually impact or elongation - the cosmetic requirement, the colour tolerance, the food-contact or VOC status, and the annual volume. With that we can propose a ratio and a source rather than a slogan, say whether the existing tool can absorb the shrinkage and flow change, and quote the part so that the extra inspection and the re-validation are visible rather than discovered at the trial shot. See plastic injection molding for the process, surface finishing for how moulded colour and texture affect recyclate appearance, and metal stamping where a metal part sidesteps recycled-content targets altogether. Ask for a recycled-content proposal for your part Scope and sources. Regulatory thresholds and property bands were compiled in 2026 from a summary of the EU packaging regulation recycled-content articles with the 2030 and 2040 minimum percentages, a breakdown of article 7 PCR targets by packaging category and the certificate routes that document them, an analysis of recycled-content requirements for vehicles including the 2030 threshold, marking rules and VOC testing, a review of recycled polymer processing covering regrind, recycled polycarbonate drying limits and recycled PET heat resistance and a technical note on the variability and contamination risk of post-consumer recyclate in compounding. Property-retention figures are indicative industry experience for the same nominal grade and vary widely by waste stream, processing history and supplier; they are planning ranges, not specifications. Regulatory dates and percentages were current when compiled and should be re-checked against the consolidated regulation text before a compliance decision.

The short answer Water in the pellet turns to steam at melt temperature and breaks the polymer chains, so wet resin produces silver streaks, bubbles, a dull surface and measurably weaker parts. Hygroscopic resins - PA, PC, PBT, PET and to a lesser degree ABS - must be dried to a stated limit, typically 0.01 to 0.10 percent, before moulding. Hygroscopic versus non-hygroscopic resins The dividing line is whether water dissolves into the polymer or only sits on the surface of the granule. Polypropylene and polyethylene are effectively non-hygroscopic: they pick up surface moisture, which is easy to drive off, and in normal conditions they can be moulded straight from a sealed bag. Polystyrene, PVC and PMMA sit in between. Nylon, polycarbonate, PBT, PET, PPS, PEEK and TPU are genuinely hygroscopic, and water absorbed into the pellet does not come off in a hopper at production temperature - it needs a defined drying cycle in the right kind of dryer. The trap is that a wet pellet looks and feels exactly like a dry one. There is no visible warning until the parts come out streaked. What the water actually does: hydrolysis At 200 to 300 C, absorbed water is no longer a passive filler. It attacks the polymer backbone in a reaction called hydrolysis, cutting long chains into shorter ones. The molecular weight drop is what does the damage, because impact strength and elongation depend far more on chain length than on any additive. The visible result is often only cosmetic, which is why the mechanical loss is so easy to miss: a part can look acceptable after a quick wipe and still fail a drop test it would previously have passed. Polyester and polyamide families are the most sensitive because the same ester and amide bonds that give them their properties are exactly the bonds water attacks, which is also why over-drying is not a safe answer - heat and time degrade them too. Hydrlysis is a chain-length problem first and a cosmetic problem second. The defects you will see first Splay and silver streaks. Glossy, silvery lines radiating from the gate, where steam has flashed and stretched the melt. This is the classic wet-material signature and it appears on the first cosmetic part. Bubbles and internal voids. Trapped steam expands inside thicker sections and leaves holes that may not break the surface. On a pressure-tight part this is a functional failure, not a cosmetic one. Dull, cloudy or mottled surfaces. A wet material rarely fills and packs the same way, so gloss drops, weld lines become visible, and transparent parts come out hazy. Loss of impact and tensile strength. The reduction is real and permanent because it is molecular. It is typically 10 to 30 percent on a badly hydrolysed engineering resin, and it shows up in service rather than on the production line. Dimensional drift and warpage. Reduced melt viscosity and unstable packing change shrinkage, so a part that was in tolerance last week drifts out of it. Nozzle drool and screw slip. In severe cases the gas pocket at the front of the screw disrupts the shot and the machine cannot hold a stable cushion. That is usually when the cause is finally investigated. Recommended drying setpoints Drying is defined by three numbers: temperature, time and a target moisture level. All three must be right, because drying at the correct temperature for too short a time leaves water in the core of the pellet, and drying at too high a temperature damages the resin while the moisture reading looks correct. ResinDrying temperatureTimeTarget moistureDryer PA6, PA6680 to 90 C4 to 6 hours0.10 percent or lessDesiccant, dew point -30 C or lower PC115 to 120 C2 to 4 hours0.02 percent or lessDesiccant; keep below 130 C to avoid yellowing PBT120 to 130 C3 to 4 hours0.02 percent or lessDesiccant PET150 to 160 C4 to 6 hours0.01 percent or lessDesiccant or vacuum; dry-air conveying ABS80 to 90 C2 to 3 hours0.10 percent or lessHot air is usually enough; desiccant for cosmetic parts POM80 to 85 C2 to 3 hours0.02 percent or lessHot air; do not overheat PP, PE60 to 80 C1 to 2 hourssurface moisture onlyUsually not required Temperature, time and a moisture target. Two out of three is not drying, it is a guess. PET is the strictest of the common resins at 0.01 percent, an order of magnitude below nylon. Dryer selection and the dew point rule For low-hygroscopic resins a conventional hot-air dryer is adequate. For PA, PC, PBT, PET, PPS and TPU, hot air cannot get below ambient humidity, and in a humid climate it will not reach the target moisture at all: those materials need a desiccant dryer or a vacuum dryer holding a dew point of -30 C or lower, with -40 C as a better working target. Practical settings matter as much as the machine: air speed around 2 to 3 m/s so the hot air actually penetrates the bed, a hopper temperature held within about 5 C, and a bed depth matched to the dryer so the top and bottom of the charge dry equally. In the rainy season extend the cycle by 20 to 30 percent. Nylon that has been exposed to open air for more than about 15 minutes should be re-dried before use, and re-dried material always needs a fresh drying cycle because regrind absorbs moisture faster than virgin pellets. Over-drying is a real failure mode Yellowing and discolouration. Transparent polycarbonate held above about 130 C turns yellow, and no amount of process tuning brings it back. Additive loss. Plasticisers, lubricants and flame retardants can migrate or degrade, so a correctly dried resin can still lose the property the additive was there to provide. Viscosity and flow changes. Thermal degradation lowers melt viscosity, which changes fill pressure, flash and dimensional behaviour, and POM in particular can release irritant formaldehyde vapour if overheated. Sticking and caking. Softening at the top of the window makes pellets clump in the hopper and feeds unevenly. The safe rule. Keep the drying temperature at least 20 to 30 C below the melting point and 5 to 10 C below the onset of thermal decomposition, and treat the supplier's temperature and time as a window rather than a suggestion. Verify dryness, then keep it dry Drying without verification is optimism. The reliable shop-floor check is a moisture analyser working by loss-on-drying, or a dew point meter on the dryer outlet. A quick process check is a short shot: inject a partial part and look for splay, bubbles or steam at the nozzle, then re-check after any break in production. Once the material is dry it has to stay dry, which means sealed hoppers, dry-air conveying rather than an open bucket, loadings matched to consumption so nothing sits in the hopper overnight, and first-in first-out stock rotation. Many apparent machine faults - short shots, streaks, weak parts - are actually a drying audit, and the cheapest fix in a moulding shop is usually a closed loop between the dryer and the press. Send us the resin and the cosmetic requirement and we will confirm the drying route, the target moisture and the risk to the finished part. See plastic injection molding for the process, surface finishing for what splay and dulling do to a cosmetic surface, and aluminium die casting where a metal part avoids the drying question entirely. Ask us to review drying and moisture control for your part Scope and sources. Drying and moisture values were compiled in 2026 from an injection moulding temperature chart covering melt, mould and drying windows by resin, a guide to drying plastics before moulding with per-material moisture limits and the cost of over-drying, a drying condition and allowable-moisture table for common injection grades, a Chinese moulding reference on drying parameters, dew point and hopper control, a second drying reference table covering PA, PC, PBT, PET, POM, PPS and PEEK and an injection molding tolerance guide linking moisture control to dimensional consistency. Values are typical for unfilled injection grades and are planning ranges, not specifications; glass-filled, flame-retardant and reprocessed materials often need a longer cycle. Always follow the resin supplier's datasheet for the exact grade.

The short answer Yes, with limits. Bio-based drop-in grades such as bio-PE, bio-PET and bio-PA run on standard injection molding equipment with the same settings as their fossil twins. PLA, PHA, PBS and starch blends mould too, but they need their own mould temperatures, drying and cycle settings, and PLA softens near 60 C, so hot-fill and under-hood use are out. Bio-based and biodegradable are two different questions Buyers routinely treat these as one word, and that is where specifications go wrong. Bio-based means the carbon came from a plant rather than from oil or gas. Biodegradable means the material can be broken down by micro-organisms under stated conditions. A bio-based polymer can be non-biodegradable, and a fossil-based polymer can be compostable. Bio-polyethylene and bio-PET are chemically identical to their petrochemical versions and will persist in the environment exactly as long as they always have. PLA is both bio-based and compostable, but only industrially. PHA is bio-based and degrades in home compost, soil and marine environments. If the requirement is a lower carbon feedstock, ask the first question. If the requirement is end-of-life, ask the second, and ask where the degradation has to happen. Feedstock and end-of-life are independent properties. A specification has to state both. The drop-in options: bio-PE, bio-PET and bio-PA These are the easiest route into a bio-based part because nothing about the mould, the machine or the processing window changes. Bio-polyethylene is made from sugar-cane ethanol and is a drop-in replacement for fossil PE at the same density, shrinkage and melt behaviour. Bio-PET substitutes bio-based monoethylene glycol and, in some grades, bio-based purified terephthalic acid. Bio-polyamides from castor oil replace PA6, PA11 or PA12 in technical parts with comparable or better properties, including lower moisture uptake than PA6 in the case of the long-chain grades. The trade-offs are commercial rather than technical: a price premium over fossil equivalents, and a supplier base that is smaller, so lead time and minimum order quantity have to be checked before a programme depends on it. The new polymers: PLA, PHA, PBS and starch blends These are the materials that behave differently, and each has a distinct position. PLA. The volume leader in rigid compostable parts. It is stiff and strong, with tensile strength around 60 MPa, close to polystyrene, and it is transparent. Its glass transition sits between 55 and 65 C and its heat deflection temperature around 55 to 60 C, which is the single biggest constraint: a PLA container distorts in a hot car or under hot food. Its melting range is roughly 170 to 180 C and it moulds between about 170 and 210 C, with mould temperatures of 80 to 120 C and often a hot runner or hardened, chromium-plated tooling to avoid sticking. PHA. Produced by bacterial fermentation, it is the most versatile of the degradable family, ranging from stiff to rubbery depending on copolymer, with heat resistance that can reach around 120 C in some grades and genuine home-compost, soil and marine certification. The obstacles are cost, around USD 8,500 to 9,940 per tonne or roughly twice PLA, a narrow melt window in the region of 130 to 180 C with degradation risk at the top of it, shorter shelf stability, and a moulding cycle about 4 to 6 seconds longer than polypropylene on comparable parts. PBS and PBAT. PBS behaves much like polypropylene, with a melting point around 115 C, a heat deflection temperature near 100 C and tensile strength around 40 MPa, and it moulds on conventional equipment. PBAT is the flexible member of the group, with elongation above 700 percent, and is used where toughness or film behaviour is needed. Both are usually blended rather than used alone. Starch blends. Cheap and genuinely compostable, but mechanically weak and moisture sensitive. They mould thick, short-flow parts such as disposable cutlery and trays, with starch contents above 60 percent, and they need careful drying because the material takes up water readily. PHA has the narrowest window. On that material, residence time and barrel temperature control matter more than on any conventional resin. Where bio-based plastics sit in the market The market is real but still small, and knowing the scale helps set expectations on supply. Bio-based plastics production capacity was around 2.31 million tonnes in 2025, against roughly 431 million tonnes of plastics produced worldwide, or about 0.5 percent of the total, and it is forecast to reach about 4.69 million tonnes by 2030. Industry capacity utilisation was about 72 percent in 2025, which means the constraint is demand and cost more than technology. Packaging is the largest segment at about 41 percent of capacity, or 0.95 million tonnes, followed by textiles, consumer goods and automotive at roughly 0.24 million tonnes. PLA alone accounts for around a quarter of capacity, and polyamides, PTT and bio-PE follow. The practical consequence for a programme is that a bio-based grade may carry a longer lead time and a higher minimum order quantity than the commodity resin it replaces, and that only a few suppliers will hold stock. PHA carries a large premium over PLA, which is why PLA dominates rigid compostable parts today. The limits you have to design around Heat is the first limit for PLA. Softening near 60 C rules out hot-fill, dishwashers, vehicle interiors and anything near a heat source unless the part is crystallised or annealed, which changes the tool and the cycle. Composting needs infrastructure. PLA is certified for industrial composting to EN 13432 and ASTM D6400, requiring temperatures of about 58 C or more, and it degrades very slowly in home compost, soil or landfill. A part labelled compostable that goes to landfill behaves like a conventional plastic. Degradable grades can contaminate recycling. A compostable item wrongly placed in the PET recycling stream degrades the recyclate. That is a labelling and collection problem as much as a materials one, and it is a reason some brand owners choose bio-based but non-degradable drop-ins instead. Impact resistance is usually lower. PLA is brittle, with elongation at break of only a few percent, so anything that is dropped, snapped or hinged needs a blend, a rubbery grade, or a different polymer. Drying and thermal control are strict. PHA and starch blends take up water quickly and are sensitive to shear heat. Desiccant or vacuum drying and controlled residence time are not optional extras. Regulatory approval is per grade. Food contact and medical status depend on the specific grade and the migration limits that apply, not on the polymer family. Compostability claims also have to name the standard and the environment. Tooling may differ. The higher mould temperatures PLA wants, and the sticking tendency of some grades, can mean hardened and polished tool steel rather than the plain P20 used for a commodity resin. How to specify a bio-based part without a surprise Tell us which requirement is driving the change: a lower-carbon feedstock, a compostable end-of-life claim, a specific regulatory target, or a consumer-facing label. Then give the service temperature, whether the part is hot-filled or dishwasher-cleaned, the impact and drop requirement, the required compostability standard and the disposal environment, the food-contact status, the expected annual volume and the acceptable price premium. With that we can say whether a drop-in bio-grade keeps the existing tool and settings, or whether a new polymer is needed and what it changes in mould temperature, drying, cycle time and tooling. See plastic injection molding for the process, FDM 3D printing for the prototyping route that runs PLA best, and surface finishing for decoration and texture on bio-based parts. Ask which bio-based grade fits your part Scope and sources. Property, price and market figures were compiled in 2026 from the European Bioplastics market development update for 2025, covering global capacity, utilisation and segment shares, a technical comparison of PLA, PHA, PBS and PBAT with melting points, tensile strength and price ranges, a PLA versus PHA selection guide covering thermal properties, processing windows and composting certification, an analysis of biodegradable rigid packaging including PLA share, heat deflection and PHA cycle times, a review of environmentally friendly polymers in injection moulds covering PLA and PHA mould temperatures and starch blends and the European Bioplastics FAQ on bioplastic definitions, capacity data and substitution potential. Prices are indicative 2026 bands for small-to-medium lots and move with feedstock and capacity. Compostability and food-contact claims depend on the specific grade and certificate; confirm both against the supplier datasheet before committing a programme.

The short answer Choose from the part's duty, not from a price list. Fix the operating temperature range first, then chemical, UV and moisture exposure, then load, impact and creep, then appearance and regulation, and only then cost. The resin family falls out of that sequence; it should never be the starting point. Filter on duty before you open a datasheet Most material mistakes are made in the first five minutes, when a familiar or cheap resin is chosen and the requirements are reverse-engineered afterwards. The order below costs an hour and can save a mould. Temperature comes first because it removes more resins than any other single factor. A datasheet heat deflection temperature is measured under a stated load, usually 0.45 MPa or 1.82 MPa, and it is not the same as the temperature at which the part stops working. Write down the continuous service temperature, the peak excursion and how long the peak lasts before you compare anything else. A garden-tool housing that reaches 60 C on a hot day and a bracket bolted to a gearbox at 120 C are not in the same selection exercise at all. Each stage removes candidates. Skipping a stage is how a part ends up in the wrong resin. Temperature alone usually cuts the list from twenty resins to four. Chemicals, UV and moisture come second Environment is where the second round of candidates falls away, and where the cheapest option is often disqualified. Chemical exposure. Polypropylene and polyethylene resist most aqueous chemicals, alcohols and detergents and are the default for cleaning products and medical fluid handling. Polycarbonate is strong and transparent but is vulnerable to solvent crazing and to alkaline cleaners, and it can fail by environmental stress cracking at loads far below its tensile limit. Any part that will be wiped with a solvent needs the specific chemical listed on the drawing, not the word chemical-resistant. UV and weather. Unprotected ABS yellows and chalks outdoors because its butadiene phase degrades in sunlight. ABS used outside needs a UV-stabilised grade, an opaque coating, or a swap to ASA, which keeps ABS's appearance and processing behaviour with a weather-resistant rubber phase. Moisture in service. Nylon absorbs water from the air, and a moulded PA6 part can pick up around 2 to 3 percent of its own weight over time, which moves dimensions and softens the part. For a tight-tolerance assembly in a humid climate that is often enough to disqualify nylon in favour of POM or PBT, which take up far less water. Contact and hygiene. Food contact, skin contact and medical use are grade-level questions, not family-level ones. General-purpose ABS and polystyrene are normally not approved because of residual monomer, while food-contact grades of PP, PE, PET and PC exist and have to be named explicitly. Then the mechanical duty Tensile strength on a datasheet is the least useful number in isolation. For a part that is loaded once and never again, static strength governs. For a bracket, a clip or a pressurised housing, creep under sustained load governs, and creep is a function of temperature and time rather than of short-term strength. For anything that is snapped together repeatedly, fatigue and notch sensitivity govern. The spread inside one family is large: unfilled polypropylene sits around 30 to 40 MPa tensile, ABS around 40 to 50 MPa, polycarbonate around 60 to 70 MPa, POM around 60 to 70 MPa with excellent fatigue life, and a 30 percent glass-filled PA66 reaches roughly 150 to 180 MPa with a modulus in the 8,000 to 10,000 MPa range. Glass fibre also brings rules of its own: it is abrasive, so gate inserts wear, and it reduces and directs shrinkage, which changes the tool more than it changes the part drawing. Appearance, regulation and cost come last Cosmetics are a material decision because they interact with every earlier stage. A painted part needs a substrate that takes paint without plasma or flame pre-treatment, which points to ABS, PC or a PC/ABS blend and away from the olefins. A plated bezel needs an ABS plating grade rather than a general-purpose one, because those grades are formulated for metal adhesion. A moulded-in-colour outdoor panel points to ASA so that painting is not needed at all. Regulation narrows the list again: a flame-retardant grade is required for an electrical enclosure, it costs materially more than the general-purpose grade, and it runs in a different processing window. Cost belongs at the end of the sequence, not the beginning, because the total cost of a part is dominated by the wall thickness, the cycle time and the scrap rate that the resin decision implies. As a rough planning rule, polypropylene runs around USD 1.2 to 1.8 per kilogram, ABS around 2.0 to 2.6, polycarbonate around 3.0 to 4.0 and glass-filled PA66 around 4.0 to 5.5, so a resin that costs twice as much per kilogram is rarely the reason a part is expensive or cheap. Five resins cover the great majority of commercial parts. Start here, then move up only for a stated reason. The shortlist in practice Once the four stages are written down, the shortlist is usually two or three resins, and the remaining work is on the drawing rather than in the material catalogue. RequirementPoints toWatch out for Cheap, chemical-resistant, no cosmeticsPP homopolymer or copolymer1.5 to 2.0 percent shrinkage, cannot be painted or glued without pre-treatment Good looks, tough, easy to paint or plateABS, or PC/ABS where heat is shortUV degradation outdoors, solvent sensitivity, drying before moulding Transparent and impact resistantPC or PMMAPC is notch sensitive and needs a 120 C dry; PMMA is brittle Stiff, hot, chemically aggressivePA66-GF30, PBT-GF30, PPSAbrasive to tooling, anisotropy from fibre orientation Tight tolerance moving partsPOM, PBT, PPSPOM releases formaldehyde if overheated, so corrosion-resistant tool steel Outdoor, moulded-in colourASA, or a weatherable PC blendHigher price than ABS for the same geometry Limits: when the right resin is still the wrong part The material cannot rescue a design, and it cannot be swapped late without consequence. Shrinkage is a tooling number. A part dimensioned for ABS at 0.5 percent shrinkage is undersized if the resin is changed to PP at 1.8 percent without reworking the cavity. Material changes after tool approval are one of the common causes of a full cavity replacement. Wall thickness rules win. Most resins are comfortable between roughly 1.0 mm and 3.5 mm. Below that, flow and strength suffer; above it, cooling time, sink marks and warpage dominate and no resin choice fixes it. Ribs at 50 to 70 percent of the nominal wall and a draft of at least 1 degree per side matter more than the brand of resin. Some families need their own equipment. PVC and some thermoplastic elastomers need corrosion-resistant barrels and tooling, and POM needs good venting and corrosion-resistant steel because it releases formaldehyde when overheated. Drying is not optional. PA, PC, PBT and PET are hygroscopic and must be dried to a stated moisture level before moulding. Skipping it produces splay, voids and a measurable loss of strength. Fire, food and medical ratings are grade-specific. A flame-retardant version of a resin is a different product with a different price and processing window. Never assume the general-purpose grade carries the approval. Optics and wear have ceilings. PC and PMMA both scratch. If a lens has to survive abrasion, the answer is usually a coating or a different material system, not a thicker part. Turning the shortlist into a quoted part A comparable quotation needs the resin named and the reason recorded. Send the 3D model and the 2D drawing with the continuous and peak service temperature, the chemicals and cleaners the part will meet, whether it lives indoors or outdoors, the load and whether it is sustained or intermittent, which surfaces are cosmetic and to what finish, and any flame, food, medical or VOC requirement that applies. With that we can name a grade rather than a family, flag the shrinkage and ejection implications before the tool is cut, and price the part so that the wall thickness and cycle time are visible on the page rather than discovered at the trial shot. See plastic injection molding for the process and its design rules, surface finishing for painting, texturing and plating, and metal stamping where a formed metal part competes with a moulded one. Send a part for resin selection and a quote Scope and sources. Property and cost bands were compiled in 2026 from a plastic material selection guide with a PP, ABS, PC, PA66-GF30 and POM property table, a resin selection guide covering heat deflection, price and the failure modes of each family, a resin selection decision tree linking shrinkage to cavity dimensions and tool steel, an automotive material selection framework covering temperature, chemical and regulatory filters, an injection molding tolerance guide covering wall thickness, draft, venting and process stability and an injection moulding design guide with recommended wall thickness by resin. These are planning ranges for general-purpose grades, not quotations or guarantees; flame-retardant, glass-filled, impact-modified and food-contact grades sit outside them. Confirm the exact grade, shrinkage and drying requirement against the supplier datasheet before releasing a mould.

The short answer ABS is popular because one resin delivers impact toughness, a glossy moulded surface and easy processing at a mid-range price. It runs at 210 to 250 C with a wide process window, holds 0.4 to 0.7 percent shrinkage, and accepts paint, plating, gluing and ultrasonic welding better than most plastics. Its limits are UV, heat near 90 C, solvents and flammability. Three monomers, three jobs ABS is a terpolymer, and its reputation for balance comes directly from what each of the three monomers contributes. Remove any one and the material loses a property that buyers rely on. Each monomer covers a weakness that the other two would leave open. Acrylonitrile is the rigid, chemically resistant component and it raises heat stability. Butadiene is a rubber phase grafted into the chain, and it is what absorbs impact energy rather than cracking. Styrene lowers the melting temperature and improves flow, which is where the glossy, easily moulded surface comes from. The result is a material that is not the strongest, stiffest or most heat-resistant plastic available, but is good enough at all of those simultaneously - which is exactly what a consumer enclosure or a power-tool housing needs. The property set that makes it a default PropertyTypical unfilled ABSWhy it matters Density1.04 to 1.06 g/cm3Mid-range part weight for a rigid housing Tensile strength40 to 45 MPaAdequate for enclosures, brackets and trim Notched impact150 to 250 J/mSurvives drops and knocks at room temperature Heat deflection88 to 100 C at 0.45 MPaFine indoors; marginal near motors and lamps Glass transition105 to 115 CSets the ceiling for any load-bearing use Shrinkage0.4 to 0.7 percentLow and predictable, so dimensions hold Service rangeAbout -40 to 80 CWide enough for most indoor duty Melt temperature210 to 250 CRuns on standard machines and tool steel Mould temperature40 to 80 CShort cycle, low energy per part Indicative priceUSD 2.00 to 2.60 per kgCommodity-adjacent rather than premium ABS is not the toughest resin, but it is the toughest one at its price. Processing is forgiving A material that processes easily is worth more than its datasheet suggests, because it produces fewer defects, less scrap and shorter cycle times. ABS sits at the forgiving end of the spectrum. Its melt temperature of 210 to 250 C is comfortably below the point where ordinary P20 or 2738 tool steel becomes a concern, so the tool does not have to be built in H13 or stainless. Its mould temperature range of 40 to 80 C is broad, so gloss and dimensions can be tuned without redesigning the cooling circuit. Cycle times as low as about 20 seconds are realistic on small parts, and scrap rates on a stable mould are below 1 percent. There is one process step that cannot be skipped. ABS is hygroscopic and will absorb moisture from the air, so pellets must be dried to under about 0.1 percent moisture, typically at 80 to 90 C for 2 to 4 hours. Moulding wet resin produces silver streaks and splay on the surface, and it reduces strength through hydrolysis. That is a standard quality question to ask about any supplier running ABS for cosmetic parts. A mid-range melt temperature and a forgiving mould temperature are much of the reason ABS is easy to run. Secondary operations are where ABS really wins This is the advantage buyers notice last and value most. ABS takes a clean, stable surface straight out of the tool, and it accepts almost anything you then want to do to it. It can be painted without aggressive surface preparation, electroplated to a bright chrome or nickel finish, solvent or ultrasonically welded, laser marked and glued with standard adhesives. Olefin resins such as PP and PE cannot do most of this without flame or plasma pre-treatment, which is why a product needing a plated bezel or a welded housing tends to end up in ABS. When a part must be chrome finished, an ABS plating grade is usually the correct specification rather than a general-purpose one, because those grades are formulated for adhesion. The limits you have to design around Heat. Unfilled ABS deflects around 88 to 100 C and softens above about 80 C under load. It is not suitable for anything near a motor, a lamp or an exhaust path. Heat-resistant grades reach above 110 C but they cost more and process differently. UV and weather. The butadiene phase degrades in sustained sunlight, so unprotected ABS yellows, chalks and eventually becomes brittle outdoors. The options are a UV-stabilised grade, an opaque coating, or a switch to ASA or a weatherable PC blend for a part that genuinely lives outside. Solvents, ketones and esters. ABS is vulnerable to many solvents and can fail by environmental stress cracking at loads far below its mechanical limit. Any part exposed to cleaning agents, fuels or adhesives needs the chemical exposure checked before the resin is approved. Flammability. General-purpose ABS burns. Anything in an electrical enclosure that must meet UL 94 V-0 needs a flame-retardant grade, which is more expensive and has a different processing window. Strength ceiling. Tensile strength around 40 to 45 MPa puts ABS firmly in the mid range. High static loads or elevated temperatures belong to glass-filled nylon or polycarbonate. Food contact. Most general-purpose grades are not approved for food contact because of residual styrene monomer. Food-grade grades exist, but they have to be specified explicitly. Grades, and when to step up to PC/ABS or ASA Writing ABS on a drawing is not enough for a comparable quote, because the family contains grades that behave quite differently. Impact grade. High-impact grades above roughly 39 kJ/m2 for helmets, luggage and rugged tool housings; medium grades for appliances and automotive interior parts. Flow grade. High-flow grades fill thin walls and long flow paths, at some cost in impact strength. Thin cosmetic shells usually need this. Plating grade. Formulated so electroplated metal adheres reliably. Specifying a general-purpose grade for a plated part is a common and expensive mistake. Flame-retardant grade. Required for electronics enclosures meeting UL 94 V-0, and materially more expensive. Blend or alternative. Where ABS is nearly right but heat or impact is short, a PC/ABS blend adds both for a modest cost increase. Where UV is the problem rather than heat, ASA is the direct swap, because it keeps ABS's appearance and processing behaviour with a weather-resistant rubber phase. Getting an ABS part quoted properly ABS is a tailored material, so the grade, the polish and the drying step all belong in the specification. Tell us which surfaces are cosmetic and what finish they need - an SPI polish number or a texture reference - whether the part will be painted, plated or welded, the continuous and peak service temperature, and whether any flame or food-contact rating applies. With that we can name a grade rather than a family, flag the shrinkage and ejection implications, and price the part so the finishing steps are visible rather than discovered later. See plastic injection molding for the process, surface finishing for painting, texturing and electroplating, and metal stamping where a formed metal part competes with a moulded one. Send a part for ABS grade selection and a quote Scope and sources. Composition, mechanical, thermal and processing values were compiled in 2026 from an ABS buyer's guide covering monomer roles, processing window and limitations, an ABS material and process guide covering thermal properties, drying and secondary operations, a guide to ABS grades with impact and heat deflection values by grade, a thermoplastic comparison table placing ABS against PP, PE, PC, POM and PMMA and a comparison of ABS with polypropylene and polycarbonate. Values are typical for general-purpose unfilled grades; flame-retardant, glass-filled, heat-resistant and plating grades sit outside these ranges. Confirm the exact grade, shrinkage and drying requirement against the supplier datasheet before releasing a mould.

The short answer Injection molding runs three tiers of plastic. Commodity grades - PP, PE, PS and ABS - cover most packaging, housings and consumer parts at USD 1.20 to 2.60 per kilogram. Engineering resins - PC, PA, POM and PBT - add strength, heat resistance and dimensional stability. High-performance grades such as PPS, PEEK and PPSU serve under-hood, aerospace and medical duty. Three tiers, not one long list A supplier will happily list twenty resins, which does not help a buyer choose. It is more useful to sort them by what they cost and what they tolerate, because price and capability rise together. Commodity resins are produced in the largest volumes and priced lowest: polypropylene, polyethylene, polystyrene and ABS. They are strong enough for the great majority of enclosures, containers, caps and housings, and they are forgiving to mould. Engineering resins cost two to four times more and are chosen for a specific property that a commodity grade cannot deliver: the impact and clarity of polycarbonate, the wear and dimensional precision of acetal, the strength and fatigue resistance of nylon, or the electrical and thermal stability of PBT. High-performance resins such as PPS, PEEK, PEI and PPSU sit above that, at multiples of engineering prices, and are justified only where continuous temperature, chemical exposure or a regulatory requirement rules everything else out. The commodity workhorses Eight resins cover the great majority of commercial moulded parts. Polypropylene (PP). Density 0.90 g/cm3, tensile 32 to 40 MPa, heat deflection 95 to 105 C and shrinkage 1.5 to 2.5 percent. It has the best chemical resistance of any low-cost resin and survives millions of flex cycles, which is why living hinges and fluid containers are almost always PP. The price is high and anisotropic shrinkage, so flat PP parts need generous radii and careful gating to stay straight. High-density polyethylene (PE-HD). Tensile 26 to 33 MPa, very low moisture sensitivity and excellent chemical resistance. It is the material for bottles, caps, closures and chemical tanks. It is soft and low-stiffness, and it releases dimensionally poorly, so it is rarely used for precision parts. Polystyrene (PS). Cheap, rigid and optically clear in its general-purpose form, and easily foamed. It is brittle, has poor chemical resistance and burns readily, which limits it to disposables, laboratory ware and packaging. ABS. Tensile 40 to 45 MPa, deflection 88 to 100 C, shrinkage 0.4 to 0.7 percent. It is the cosmetic default because it moulds with a clean, gluable, paintable, plateable surface, and it takes impact well at room temperature. Its weaknesses are UV, heat above roughly 90 C and solvents. PMMA (acrylic). Tensile 60 to 70 MPa with glass-like clarity and outstanding weathering, but brittle and easily scratched. Lenses, light guides, displays and protective covers are its territory. The engineering resins These are specified when one property genuinely has to be better than a commodity grade can deliver, and the price difference is the cost of that single requirement. Polycarbonate (PC). Tensile 60 to 70 MPa, notched impact 600 to 800 J/m and deflection 125 to 140 C. Optical clarity around 88 percent light transmission and impact toughness that no commodity resin approaches make it the material for safety equipment, lenses and transparent guards. It is notch sensitive, susceptible to solvent crazing and needs higher melt temperatures than ABS. Nylon - PA6 and PA66. Tensile 60 to 80 MPa unfilled, rising to 150 to 180 MPa with 30 percent glass fibre, with excellent wear and fatigue behaviour. Nylons absorb moisture, which changes dimensions in service, so they are specified for gears, bearings and brackets where toughness matters more than dimensional stability. Acetal (POM). Tensile 60 to 75 MPa, low friction, high stiffness and very low moisture pickup, which makes it the easiest resin for tight-tolerance moving parts. It is the grade to specify when a plastic part has to do the job of a metal one. Watch for notch sensitivity, centreline porosity in sections over about 6 mm, and formaldehyde release that requires corrosion-resistant tool steel. PBT and PET. Dimensionally stable and electrically robust, with low moisture absorption. Automotive connectors, sensor bodies and electrical housings are the classic applications. High-performance resins and soft-touch grades Price spreads five-fold across these grades, and far more once PEEK is on the table. At the top of the range sit PPS, PEI, PPSU and PEEK, which hold properties above 150 C continuously and resist fuels, solvents and sterilisation. PEEK costs well over USD 50 per kilogram, requires barrel temperatures of 350 to 400 C and abrasive glass or carbon fillers in many grades, so it is only justified where a regulatory or performance requirement leaves no alternative - typically aerospace brackets, semiconductor parts and medical implants. At the other end of the hardness scale, TPE and TPU are the soft-touch resins used for grips, seals and overmoulded surfaces, chosen for adhesion to a rigid substrate as much as for their own properties. Glass fibre is the largest single property jump available, and the largest change in tool wear. How to choose: four questions in order What temperature does the part see? Service temperature eliminates more resins than any other single question. Continuous exposure above about 100 C rules out standard ABS, PP and PE; above 150 C only the high-performance tier remains. What is it exposed to? Oils, fuels and solvents drive the choice toward semi-crystalline resins such as PP, PA and POM. Direct sunlight rules out unmodified ABS and PC unless they are UV stabilised or painted. What does it have to do mechanically? Sliding and precision motion points to POM or PA. Drop and impact protection points to PC or a PC/ABS blend. Repeated flexing points to PP. High static load without heat points to a glass-filled grade. Only then look at price and process. Compare resin cost against cycle time, yield and secondary operations together rather than on unit price alone, because a cheaper resin that needs a longer cycle or extra finishing is not cheaper. Where the choice goes wrong Writing the resin family instead of the grade. One family contains dozens of grades with different flow, heat resistance, flame rating and glass content. Naming ABS or PC is only the first step, and it is the step that most often produces a quote for the wrong part. Changing resin after the tool is cut. Shrinkage alone changes every cavity dimension. A part dimensioned for ABS at about 0.5 percent shrinkage will be undersized if it is switched to PP at about 1.8 percent without reworking the cavity, and in practice that can mean a replacement cavity. Assuming a flame rating is included. General-purpose ABS and PP are flammable. UL 94 V-0 needs an FR grade, which costs more and often moulds differently, so it has to be in the original specification. Forgetting moisture. PA, PC, ABS and PBT are hygroscopic. Moulding them wet produces splay, silver streaks and reduced strength, so drying is part of the quoted cycle whether or not it appears on the drawing. Over-specifying on a cosmetic part. Putting a high-performance resin on a visible cover that never sees heat or chemicals buys nothing and costs real money, and often processes less attractively than ABS or a PC/ABS blend. From a resin family to a real grade The fastest route to a correct quotation is to describe the part's duty rather than naming a resin. Tell us the continuous and peak service temperature, the chemicals or UV exposure it will see, the load and whether it is static, sliding or impact, the wall thickness, whether it must be transparent or plated, and any food-contact, flame or medical requirement. With that we can shortlist two or three grades, flag the shrinkage, drying and tool-steel implications of each, and price the part so the resin choice is visible in the total cost rather than only in the material line. See plastic injection molding for the process, surface finishing for paints, textures and plating, and aluminium die casting where the part should be metal. Send a part for resin selection and a moulding quote Scope and sources. Property values, application notes and price bands were compiled in 2026 from a thermoplastic comparison table covering PP, PE, ABS, PC, POM, PMMA and TPU with heat deflection and shrinkage, a material selection guide for PP, ABS, PC, PA and POM with processing windows and 2026 prices, a resin selection reference covering cost, heat deflection and tool-steel implications and a thermoplastic selection framework covering environment, load and cost. Values are typical for general-purpose unfilled grades: glass-filled, flame-retardant, food-contact and medical grades move outside these ranges, and actual parameters depend on the specific supplier datasheet. Confirm grade, shrinkage and drying requirements before releasing a mould design.