Choosing between POM (polyoxymethylene, also called acetal or Delrin) and PEEK (polyetheretherketone) usually comes down to one question: does the part have to survive heat, chemicals or sterilisation that would destroy an ordinary engineering plastic? If it does, PEEK earns its price. If it does not, POM will normally do the job at a fraction of the cost.
This guide compares POM vs PEEK on the properties that actually drive a machining decision — thermal limits, mechanical strength, chemical resistance, machinability and cost — and finishes with a practical selection framework you can apply to a real part.
All figures below are typical values for standard unfilled grades. Glass-filled, carbon-filled and PTFE-modified grades change these numbers substantially, so always confirm against the datasheet for the exact grade and stock shape you are buying.
Quick answer: POM or PEEK?
| If your part needs… | Choose |
|---|---|
| Continuous service above about 100 °C | PEEK |
| Autoclave, gamma or steam sterilisation | PEEK |
| Resistance to aggressive solvents, fuels or acids | PEEK |
| Maximum stiffness and low friction at the lowest cost | POM |
| Tight tolerances on a high-volume, cost-sensitive part | POM |
| Wear parts, gears, bushings, rollers, slides | POM (PEEK only if hot or sterile) |
POM vs PEEK: side-by-side comparison
| Property | POM (acetal / Delrin) | PEEK |
|---|---|---|
| Density | ~1.41 g/cm³ | ~1.30 g/cm³ |
| Tensile strength | ~60–70 MPa | ~90–100 MPa |
| Continuous service temperature | ~90–100 °C | up to ~250 °C |
| Melting point | ~165–175 °C | ~343 °C |
| Water absorption | Low (~0.2–0.3%) | Very low (<0.5%, effectively stable) |
| Chemical resistance | Good against fuels, oils, solvents; attacked by strong acids and oxidisers | Outstanding across almost the whole chemical range; a short list of exceptions including concentrated sulphuric acid |
| Wear and friction | Excellent — naturally low friction, ideal for sliding contact | Good, and better than POM at elevated temperature |
| Machinability | Very good — free-cutting, fine surface finish | Good but demanding — abrasive, sensitive to heat and notching |
| Sterilisable | No — will not survive autoclave temperatures | Yes — autoclave, steam, gamma and EtO; biocompatible grades available |
| Relative material cost | Baseline | Roughly an order of magnitude higher |
Where POM wins
POM is the default engineering plastic for mechanical parts that stay cool. It is stiff, dimensionally stable, has a naturally low coefficient of friction, and machines faster and cleaner than almost any other polymer. For gears, bushings, cams, rollers, guides, wear pads, insulators and precision mechanical components it is usually the best value on the market.
Its two weaknesses are heat and chemistry. Above roughly 100 °C in continuous service POM loses stiffness and starts to creep under load. It is also attacked by strong acids and oxidising agents, and it is not suitable for steam or autoclave sterilisation.
POM is available in two families. POM-C (copolymer) is the usual choice for machined parts because it resists hydrolysis and has better chemical resistance. POM-H (homopolymer, sold as Delrin) is slightly stiffer and harder, and takes a marginally better surface finish, but is more sensitive to acids and to moisture in service.
Where PEEK wins
PEEK is a high-performance thermoplastic, not an upgraded POM. It keeps useful mechanical strength up to roughly 250 °C in continuous service, resists nearly the entire range of industrial chemicals, absorbs almost no water, and can be sterilised repeatedly without degrading. It is also inherently flame retardant with low smoke emission, which is why it appears in aerospace interiors, semiconductor tooling, medical instruments and downhole oil and gas components.
The cost of that performance is real. PEEK stock costs roughly an order of magnitude more than POM, and it is harder on tooling and more sensitive to machining heat. Unless a part genuinely needs high temperature, chemical resistance, sterilisation or biocompatibility, you are usually paying for capability the application will never use.
How the two materials machine differently
Both are machined on standard CNC mills and lathes, but they behave very differently at the cutting edge.
Machining POM
- Cut freely and fast. POM produces short, clean chips and takes sharp tooling well. You can run high surface speeds and heavy feeds compared with most plastics.
- Control the heat. POM has a low melting point, so excessive speed or a dwell in the cut will soften the surface, weld chips to the tool and leave a smeared finish. Sharp, polished, high-rake tooling and generous chip clearance matter more than exotic grades.
- Expect some movement. POM is hygroscopic to a small degree and is not fully stress-free in extruded stock. For thin walls or tight tolerances, rough machine, stress relieve, then finish cut.
- Deburring is easy. POM takes a clean edge, which keeps secondary operations cheap.
Machining PEEK
- Use sharp, uncoated carbide with high positive rake. The standard advice for polymer cutting tools applies doubly here: a dull edge rubs, generates heat and work-hardens the surface.
- Keep the cut cool. PEEK machines best below its glass transition region. Flood coolant or strong compressed-air evacuation is normal practice, and a heavy, uninterrupted cut is better than a light rubbing pass.
- Respect its notch sensitivity. PEEK is more prone to cracking at sharp internal corners and at the edge of a machined thread than POM is. Design generous fillets and radii where you can.
- Anneal critical parts. For tight-tolerance or highly loaded components, a controlled annealing cycle after roughing relieves the internal stresses introduced during machining and reduces the risk of dimensional drift in service.
- Budget more time. Lower feeds and speeds plus annealing add machining cost on top of the higher material cost.
The cost question, honestly
PEEK is usually the correct engineering choice and almost always the more expensive one. Because stock cost dominates the price of a small machined part, switching from POM to PEEK frequently multiplies the part price several times over — before adding the extra machining time that PEEK's lower cutting speeds require.
The right question is not "which material is better" but "what is the actual service condition". If the answer is an electrical enclosure at room temperature, a gearbox bushing or a wear strip, POM is the professional choice, not a compromise. If the answer involves sterilisation cycles, hydraulic fluid at 150 °C or a semiconductor chamber, POM is not a candidate at all.
Common design mistakes
- Specifying PEEK "for safety". Overspecifying multiplies unit cost for a capability the application never exercises.
- Assuming POM is fine at 120 °C. Data-sheet heat deflection figures are measured under specific loads. Continuous service near or above 100 °C will show up as creep and loss of fit.
- Ignoring wall thickness. Both materials move after machining. Thin sections and asymmetrical geometry are far more likely to warp than the material choice is to fail.
- Designing sharp internal corners in PEEK. Notch sensitivity turns a sharp corner into a crack initiation point.
- Forgetting that finishes and fillers change everything. A glass-filled grade is stiffer and cheaper per unit volume but far more abrasive to machine and much harder to bring to a fine finish.
Frequently asked questions
Is PEEK worth the cost over POM?
Only when the application exploits what PEEK uniquely provides: continuous service above about 100 °C, repeated sterilisation, biocompatibility, or resistance to aggressive chemicals. If none of those apply, POM is the better engineering and commercial choice.
Can POM handle high temperatures?
For short excursions it will survive more than its continuous rating suggests, but sustained service above roughly 100 °C causes loss of stiffness and creep under load. For continuous high temperature, move to PEEK or a metal.
Is PEEK food-safe and biocompatible?
Yes — food-contact and implant-grade PEEK are both available, and PEEK is routinely specified for medical instruments and implants. POM is also used in food-contact applications, but it cannot be sterilised by autoclave.
Can you machine PEEK the same way as aluminium?
No. PEEK is machined with sharp high-rake tooling and controlled heat, not with the cutting parameters you would use on metal. Running aluminium speeds and feeds in PEEK will burn the surface and distort the part.
What is the difference between POM-C and POM-H?
POM-C is the copolymer, more resistant to hydrolysis and chemicals, and the usual choice for machined parts. POM-H is the homopolymer, slightly harder and stiffer with a marginally better finish, but less resistant to acids and moisture.
Does PEEK need annealing after machining?
For tight-tolerance, thin-walled or highly loaded parts, yes. A controlled post-machining annealing cycle relieves machining stress and reduces dimensional drift in service. For simple, forgiving parts it is often unnecessary.
Need a second opinion on your material choice?
We machine both POM and PEEK in production quantities — custom plastic CNC machining for everything from ABS and nylon to POM, PEEK and acrylic. Send us the drawing and the service conditions — temperature, chemical exposure, load and required life — and we will tell you honestly which material the part actually needs, then quote both options so you can see the cost difference. You can also see the grades we stock on our materials page, or compare metals in our guide to aluminium 6061 vs 7075.
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