I see a lot of RFQs where the material choice is "whatever we used last time." Sometimes that's fine. Sometimes it leaves 40% of material cost on the table or — worse — puts the wrong material in a critical application.
PTFE, PEEK, and PPS are three of the most common engineering plastics we machine. They cover different temperature ranges, chemical environments, and mechanical demands. Here's how to pick between them without staring at six datasheets for an hour.
The 30-second overview
PEEK is the strongest, toughest, and most heat-resistant of the three. Continuous use at 260°C. Excellent chemical resistance. Costs the most. Pick it when the application is demanding and cost is secondary.
PPS is the budget alternative to PEEK for moderate-temperature applications. Good chemical resistance, inherently flame retardant (V-0 without additives), and machines well. Not as tough or as heat-resistant as PEEK. Costs less than PEEK.
PTFE is the chemical and temperature champion in terms of inertness, but the mechanical weakling. Creeps under load. Can't hold tight tolerances. Unmatched friction properties. Pick it for seals, gaskets, liners, and chemically aggressive environments with low mechanical demands.
Temperature head-to-head
| Material | Continuous use | Short-term peak |
|---|---|---|
| PEEK | 260°C | 300°C+ |
| PPS | 200-220°C | 260°C |
| PTFE | 260°C | 300°C |
PEEK and PTFE tie on continuous temperature. PPS runs about 40-60°C cooler. For autoclave applications, PEEK and PPS survive repeated steam sterilization; PTFE's dimensional instability makes it less ideal despite the temperature rating.
Mechanical properties — the widest gap
PEEK is in a different league mechanically. Unfilled PEEK has 95-100 MPa tensile strength and 30-50% elongation — it's tough, not just strong. PPS is stiffer but more brittle: about 80-90 MPa tensile with 1-3% elongation. PTFE is around 25 MPa, and it creeps continuously under any sustained load.
For structural parts: PEEK. For parts that see impact: PEEK. For parts with snap-fits or live hinges: PEEK. PPS works for rigid structural parts below 200°C where cost matters. PTFE should not carry sustained mechanical load, ever.
Chemical resistance
All three are chemically resistant by normal plastic standards, but there's a hierarchy:
- PTFE: The undisputed champ. Nothing touches it except molten alkali metals and elemental fluorine.
- PEEK: Nearly as good. Concentrated sulfuric and nitric acids attack it. Most other chemicals — steam, solvents, hydrocarbons, brake fluid — do not.
- PPS: Very good below 200°C. Less resistant to strong oxidizing acids and some chlorinated organics than PEEK.
For the most aggressive chemical environments at any temperature: PTFE. For aggressive chemicals WITH mechanical load: PEEK. For moderate chemical exposure with cost constraints: PPS.
Friction and wear
PTFE is the lowest-friction solid known. Coefficient of friction: 0.05-0.10. But it wears fast. Filled PTFE (glass, carbon, bronze) dramatically improves wear at the cost of slightly higher friction.
PEEK has good wear resistance unfilled, and excellent with carbon fiber or PTFE fillers. For bearings and wear surfaces with structural load, filled PEEK is the usual choice.
PPS wear grades work for moderate loads. Not in the same tier as PEEK for dynamic wear.
Cost
PEEK costs the most — roughly 3-5x PPS and 5-8x PTFE by volume. PPS sits in the middle. PTFE is the cheapest, especially in standard virgin grades.
But raw material price is misleading. A PPS part that saves 40% vs PEEK but fails in the field costs more than a PEEK part that doesn't. Choose on requirements, then look at cost.
How we decide
- Hot + strong + chemically exposed? PEEK. It costs more because you need it.
- Hot + chemically exposed + low load? PTFE. The soft option that handles aggressive chemistry.
- Warm + chemically OK + need flame rating? PPS. V-0 without additives, good value.
- Need the lowest friction? PTFE.
- Need a bearing that carries real load? Filled PEEK.
- Budget matters and the environment isn't extreme? PPS.
We stock all three in multiple grades and machine them daily. If you're unsure which material fits your application, send the drawing and operating conditions. I'll give you a straight answer — not a datasheet comparison, but what we see working in actual parts.