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Should I use PEEK or acetal?
Use acetal for precision gears, bushings and wear parts at moderate temperatures: it machines cleanly, holds tolerances, and costs about $3 per kg versus $90–120 for PEEK. Use PEEK only when heat, steam or chemicals rule acetal out: it serves continuously to about 480 °F (250 °C) versus 212 °F (100 °C) for acetal and survives repeated steam sterilization.
PEEK (polyether ether ketone)
Acetal (POM)
By the numbers
Priced on the same representative part: housing, injection molding, 10,000 pcs.
Tensile strengthMPa
PEEK
98
POM
62
Densityg/cm³
PEEK
1.3
POM
1.41
Max service temp°C
PEEK
250
POM
100
Elongation%
PEEK
45
POM
40
Raw material cost$/kg
PEEK
100
POM
3
Which should you pick?
Pick PEEK when
- Continuous service runs above 212 °F (100 °C)
- Parts see repeated steam sterilization or hot water
- Hydrocarbons, acids or bases would attack acetal
- Flame resistance with low smoke is required
Pick POM when
- Service stays below about 212 °F (100 °C)
- You need low friction and stable dimensions at modest cost
- Parts are high-volume molded or screw machined
- The part is a snap fit, clip or plastic spring
Key differences
| PEEK | POM | |
|---|---|---|
| Molding | Melt at 700–750 °F (370–400 °C), mold at 350–400 °F (175–200 °C); few molders run it | Standard presses and mold temperatures |
| Chemical weak spots | Concentrated sulfuric and nitric acid | Strong acids, oxidizers and sustained chlorinated water |
| Steam and hot water | Handles repeated steam sterilization | Limited; copolymer resists hot water better than homopolymer |
| Flame behavior | Inherently flame resistant with low smoke | UL 94 HB in standard grades |
| Machined stock | Anneal for tight tolerances | Machines cleanly; copolymer has less centerline porosity |
| Reinforced grades | Glass- and carbon-filled grades hold stiffness at heat | Mostly used unfilled |
Questions
Why is PEEK so expensive?
The monomers and polymerization are costly and volumes are small. Resin runs about $90–120 per kg versus about $3 for acetal, and high-temperature molding and machining add more. Reserve PEEK for parts where cheaper plastics fail.
Can acetal replace PEEK?
Yes, when service stays below about 212 °F (100 °C) with no steam, strong acids or oxidizers. Some PEEK parts are specified out of caution; check the actual temperature and chemical exposure before paying for PEEK.
Is there a plastic between acetal and PEEK?
PEI (Ultem) is amorphous, serves to about 340 °F (170 °C), and costs a fraction of PEEK. It suits flame-rated housings. For chemical, wear or steam exposure, PEEK is still the better call.
Try both on your part.
The builder prices the same geometry in every suitable process and material, with DFM for each.