Comparisons / POM
PEEK vs POM (acetal)
This is the comparison that saves the most money, in both directions. Acetal is the right answer far more often than a PEEK quote suggests, and the wrong one in exactly the places where it quietly fails.
| Property | Unit | PEEK | POM (acetal) |
|---|---|---|---|
| Continuous service temperature | °C | 250 | 90 - 100 |
| Tensile strength | MPa | 90 - 100 | 65 - 75 |
| Tensile modulus | GPa | 3.5 - 4.0 | 2.8 - 3.2 |
| Thermal expansion | µm/m·K | 47 | 100 - 120 |
| Coefficient of friction | µ, dry vs steel | 0.30 - 0.40 | 0.20 - 0.35 |
| Water absorption | % at 24 h | 0.1 | 0.20 - 0.25 |
| Relative stock price | acetal = 1 | 10 | 1 |
Two rows decide most cases. Acetal stops at around 100 °C, and it expands about twice as much per degree as PEEK, which matters on a long part even at room temperature.
Choose acetal when
- The part lives below about 80 °C with margin
- Nothing aggressive touches it, and there is no steam or repeated sterilisation
- It is a mechanical part: gear, roller, spacer, manifold, fixture, guide
- You need stiffness at room temperature cheaply, since acetal is close to PEEK on modulus
- Quantity is high and material is a large share of the price
Choose PEEK when
- Continuous service passes 100 °C, or peaks do
- Steam, autoclave cycles or hot water are involved, where acetal degrades
- Acids or oxidising chemicals are present, which attack acetal readily
- The part goes into semiconductor or medical work with cleanliness and documentation requirements
- Radiation resistance matters, where acetal is one of the weakest engineering plastics
The honest cost gap
Stock is roughly ten times the price per kilo. Machining adds to it: PEEK runs slower, needs tooling kept for plastics, and thin or tightly toleranced parts pick up an annealing cycle. A finished PEEK part often lands at twelve to fifteen times the acetal equivalent.
That gap is why the substitution question is worth asking seriously rather than defensively. A hybrid assembly, with PEEK only where the heat is and acetal everywhere else, is frequently the right engineering answer and nobody proposes it because it is nobody's product.
- Where acetal is chosen wronglyNear a heater, near a motor, or in a washdown line where the cleaning chemical is stronger than anyone wrote down.
- Where PEEK is chosen wronglyRoom temperature fixtures and spacers specified in PEEK because the rest of the assembly is, which is a habit rather than a decision.
- The middle groundPPS and PEI sit between the two on both temperature and price, and are worth a look before jumping the whole gap.
- Machining timeAcetal cuts fast and cleanly. On a simple part the machining difference alone can be a third of the quote.
Questions people ask
At what temperature does acetal stop working?
Continuous service is about 90 to 100 °C. It does not fail suddenly above that, it creeps and loses stiffness, which on a loaded part looks like a dimension that drifts and a fit that loosens.
Is PEEK worth ten times the price of acetal?
Only if the part uses something acetal cannot give: temperature, steam, aggressive chemicals, radiation resistance, cleanliness for semiconductor work or load at temperature. If none of those apply, acetal is the better engineering answer, not just the cheaper one.
Which holds a tighter tolerance?
PEEK, mostly because acetal expands about twice as much per degree and absorbs a little moisture. For room temperature parts in a stable shop the difference is small, and acetal machines faster.