How to Select the Right Engineering Thermoplastic for Your Application
A practical decision framework for choosing between PEEK, Ultem, PEI, PC, nylon and acetal, without overspecifying your part into a corner.
Start with the failure mode, not the data sheet
Most engineering teams pick a resin by scrolling spec sheets and comparing tensile strength. That's backwards. The right starting point is the failure mode you're designing against.
Common failure modes in plastics parts:
- Creep under sustained load - Fatigue from cyclic loading - Wear at sliding interfaces - Stress cracking from chemical exposure - Thermal deformation above HDT - UV / hydrolysis in outdoor or wet service
Once you know the dominant failure mode, the candidate resin list shrinks fast.
## A simple decision tree
1. Continuous service above 150 °C? Look at PEEK, PPS, Ultem, PEI. 2. Sustained chemical exposure? PVDF, PEEK, PFA, avoid PC and acrylic. 3. Sliding wear surfaces? Acetal, UHMW, lubricated nylon, PEEK. 4. Optical clarity required? PC, PMMA, COC. 5. Cost-driven, indoor, moderate load? ABS, PC/ABS, PA6/66.
## Don't overspecify
We see this constantly: a customer designs a bracket in PEEK because "it's the strongest plastic we know." The part runs at 60 °C with mild static load. Glass-filled nylon would do the job at 1/15th the cost and machine faster.
> The best material is the cheapest one that survives your environment with adequate margin, not the most exotic one in the catalog.
## Talk to us early
The single biggest cost reduction in any plastic part comes from the first conversation about material. Once tooling is cut or stock is ordered, your options narrow fast. Bring us your operating envelope (temperature, load, chemicals, service life) and we'll help you land on the right grade, and the right form factor (machined, molded, extruded), to match your volume.