Guides / Materials
Where Acetal Holds Up and Where It Fails: Chemicals, Heat and UV
September 21, 2026
Most acetal parts that fail in service do not fail mechanically. They fail because the environment was not on the drawing. This guide covers what POM survives, what it does not, and how to write that into an RFQ so the quoting shop can flag a problem before you buy parts.
Temperature
Acetal is generally held to around 90 degrees C in continuous service. Homopolymer carries a slightly higher melting point than copolymer, around 175 degrees C against roughly 165, but the melting point is not the design limit. Stiffness and creep resistance fall off steadily well before it.
Two practical consequences:
- A part that is dimensionally correct at 20 degrees C will be measurably larger at 60. Thermal expansion for POM runs around 110 micrometres per metre per kelvin, roughly ten times steel. On a 100 mm part, a 40 degree rise is about 0.44 mm.
- A part that carries load at temperature creeps faster than the same part at room temperature. Preloads relax, press fits loosen.
Below zero, acetal stays usable but gets more brittle. Impact at low temperature is where notch sensitivity shows up worst.
Chemicals it handles
Acetal has good resistance to:
- Fuels, including petrol and diesel
- Most organic solvents, alcohols and ketones at room temperature
- Neutral salt solutions
- Weak alkalis, with copolymer clearly better than homopolymer
- Lubricating oils and greases
This is why POM shows up all over fuel systems and fluid handling. It is one of the few dimensionally stable plastics that does not care about hydrocarbons.
Chemicals it does not handle
- Strong acids. At any concentration worth naming, acetal is a poor choice. It depolymerises.
- Strong oxidising agents. Bleach, hydrogen peroxide at concentration, chlorine in water above trace levels.
- Strong alkalis at temperature. Copolymer copes far better than homopolymer, but a caustic clean-in-place cycle is still hard on both.
- Hot water over time. Homopolymer in particular. A part that passes a short test can fail after months of daily washdown.
If your part is going into a line that is cleaned with caustic or with chlorinated sanitiser, that belongs on the RFQ. It usually decides homopolymer against copolymer on its own.
UV and weather
Unstabilised natural acetal chalks outdoors. The surface degrades, loses strength and can shed powder. Black grades pigmented with carbon black hold up much better, and dedicated UV stabilised grades exist.
For anything outdoors, specify the grade and the colour deliberately rather than leaving colour as a cosmetic note.
Quick reference
| Environment | Acetal homopolymer | Acetal copolymer |
|---|---|---|
| Fuels and oils | Good | Good |
| Solvents at room temperature | Good | Good |
| Neutral salts | Good | Good |
| Weak alkali | Fair | Good |
| Strong alkali | Poor | Fair |
| Strong acid | Poor | Poor |
| Hot water, repeated | Poor | Fair to good |
| Steam sterilisation | Poor | Limited |
| Continuous service above 90 degrees C | Poor | Poor |
| UV outdoors, natural colour | Poor | Poor |
| UV outdoors, black or stabilised | Fair | Fair |
Treat this as orientation, not a specification. Concentration, temperature and exposure time all move the answer, and a supplier data sheet for the specific grade beats a general table every time.
Writing it into the RFQ
Three lines cover almost all of it:
Service environment: continuous 45 degrees C, occasional washdown at 70 degrees C with mild alkaline detergent. Material: acetal copolymer preferred for hydrolysis resistance. Substitution with homopolymer requires approval.
That tells a quoting shop everything it needs to either agree or push back, and it is the difference between a part that lasts and one that comes back in six months.
Not sure which grade your environment calls for? Send your RFQ with the service conditions and the shops we match will comment before they quote. Reply within 24 business hours.
Frequently asked questions
What is the maximum service temperature for acetal?
Around 90 degrees C is the usual figure for continuous service, with short excursions above that. Mechanical properties fall off well before the melting point, so treat the continuous figure as the design limit rather than the melt temperature.
Can acetal be used in hot water?
Copolymer tolerates it far better than homopolymer. Repeated hot water or steam breaks down homopolymer over time. If a part sees washdown above roughly 60 degrees C, specify copolymer and say why on the drawing.
Does acetal survive outdoors?
Not for long without help. Unstabilised acetal chalks and loses surface strength under UV. Black grades with carbon black hold up much better than natural, and UV stabilised grades exist. Outdoors is a case where the grade matters more than the family.
Need a quote for this part?
Send the drawing. We match you with up to 3 shops that machine acetal and reply within 24 business hours.
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