The short answer
Start with what the part has to survive, not with the resin name. Find your main requirement in the table below, use the guide for it, and rule out any resin that fails a second requirement. Most parts end up in one of a few families: polypropylene or polyethylene for low cost and chemicals, ABS or PC for housings, acetal or nylon for moving parts, and glass-filled or high-heat resins when load and temperature go up.
Start here: pick by what the part does
| What the part needs | Usual starting resins | Guide |
|---|---|---|
| Gears, bushings, sliding parts | Acetal, nylon; UHMW-PE for wear strips | Gears and bushings |
| Snap fits and living hinges | Polypropylene for hinges; PC, PC/ABS, nylon, acetal for snaps | Snap fits and living hinges |
| Replacing a metal bracket or housing | Glass-filled nylon, PPA, PPS; PEI or PEEK for high heat | Replacing metal |
| Hot water, steam, sterilizing | PPSU, PPS, PEEK, PVDF; PP-R and PEX for pipe | Hot water and steam |
| Outdoor and sunlight | ASA, acrylic, PVDF; UV-stabilized or black PE and PP | Outdoor and UV |
| Chemicals and solvents | PP, HDPE, PVDF, fluoropolymers, PPS | Chemical resistance |
| High heat | PPS, PEI, PEEK, PPA, glass-filled nylon | High-temperature plastics |
| Food contact | PP, HDPE, PET, copolyester; acetal and nylon for machinery | Food containers and contact |
| Electrical housings and flame ratings | FR PC, PC/ABS, modified PPE, FR PBT, FR PA66 GF | Electrical housings and UL 94 |
| Impact and toughness | Polycarbonate, PC/ABS, impact-modified PP and nylon | Impact resistance |
| Cold and freezer use | PE, impact copolymer PP, PC, TPU | Cold temperatures |
| Clear parts | Polycarbonate for toughness; acrylic for clarity, scratch and UV | Clear parts |
| Fuel, oil and hydraulic fluid | Acetal, PA11/PA12, PPS, PVDF, HDPE tanks | Fuel and oil |
| Under-the-hood automotive parts | Heat-stabilized glass-filled nylon, PPA, PPS, PBT | Under-the-hood parts |
| Electrical connectors | Glass-filled PBT and nylon; PPS, PPA, LCP for high heat | Electrical connectors |
| Medical device housings | Healthcare PC/ABS, copolyester, PPSU, PEI | Medical device housings |
| Lowest cost | Polypropylene, polyethylene, polystyrene | Engineering vs. commodity plastics |
Starting points, not final choices. Grades within a family vary widely, so check the grade’s data sheet for your conditions.
How to narrow it down
- Load and stiffness: will it carry a steady load, take impacts, or flex? Steady load at temperature points to filled engineering resins.
- Temperature: the highest temperature it sees, and for how long. Use heat deflection for short-term load and continuous use temperature for long-term life.
- Environment: water, steam, chemicals, oils, cleaners or sunlight. These rule out more resins than anything else.
- Rules: food contact, flame rating, medical or automotive specs. These limit you to specific grades.
- Appearance and tolerance: clear, glossy, painted, or tight dimensions.
- Volume and cost: compare cost per part, including density and cycle time, not just price per pound.
Tools that help
The resin selector narrows the field from two questions. The resin comparison tool puts up to three resins side by side, and resin properties by grade lists typical data sheet values. If you are matching a grade you already run, see how to find an equivalent grade. To read the numbers on a data sheet, see HDT vs. continuous use temperature, Izod vs. Charpy impact, glass transition vs. melting point and amorphous vs. semi-crystalline plastics.
What to send us
- What the part is and what it does
- The highest temperature, and any chemicals, water or sunlight it sees
- Any rules it must meet (food, flame rating, automotive spec)
- The resin you use now, if any, and what is wrong with it
- Order size and yearly usage
A polymer chemist will suggest a short list and quote it. We aim to send your quote within one to three business days.
Common questions
What is the strongest plastic?
It depends on what strong means for the part. For stiffness and strength, glass- or carbon-filled engineering resins such as PA66 GF, PPA, PPS and PEEK lead. For toughness and impact, unfilled polycarbonate is one of the best.
What is the most heat-resistant plastic for injection molding?
PEEK, PEI and PPS are the usual high-heat choices, with glass-filled PPA and nylon below them. PTFE handles more heat but cannot be injection molded like a normal thermoplastic.
What is the cheapest plastic for injection molding?
Polypropylene and polyethylene are usually the lowest cost per pound, followed by polystyrene. Cost per part also depends on density, cycle time and scrap, so compare per part, not just per pound.
Which plastic is food safe?
Many grades of polypropylene, HDPE, PET and copolyester are used for food contact, along with acetal and nylon for food machinery. Food compliance is grade by grade, so ask for the producer's FDA or EU letter for the exact grade.
Can I switch to a different plastic without changing the mold?
Sometimes, if the new resin shrinks about the same and runs at similar conditions. Check shrinkage, melt flow and drying first, then run a trial before committing.
How do I choose between two plastics?
List what the part must survive (load, heat, chemicals, sunlight, food or flame rules), rule out resins that fail any of those, then compare cost and processing on what is left. The comparison tool and guides below help with each step.
Tell us about the part
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province