Guides / Materials
Acetal or UHMW: Which Wear Plastic Belongs on Your Part
September 21, 2026
Acetal and UHMW both end up on wear part drawings, and they behave almost nothing alike. Acetal is a stiff, dimensionally stable engineering plastic. UHMW is a soft, slippery, extremely tough polyethylene. Picking the wrong one is one of the more common ways a machined plastic part fails early.
What UHMW does well
Ultra high molecular weight polyethylene has abrasion resistance that few materials touch. Chutes, hoppers, liners and guides that handle grain, gravel, glass or ore are lined with it because nothing else survives the same number of cycles.
It also absorbs impact without cracking. A UHMW guide that gets hit by a jammed product deflects and springs back. An acetal one in the same position cracks at the fixing holes.
It does not absorb water at all, and it shrugs off most chemicals.
What UHMW does badly
It is soft and it creeps. Under a sustained load, a UHMW part keeps deforming, slowly, for as long as the load is there. That rules it out for anything preloaded or anything holding a position.
It moves after machining. Machining releases stress and the part relaxes, sometimes over days. Tight tolerances are not realistic. It also has a very high coefficient of thermal expansion, roughly double acetal, so ambient temperature swings show up in the part.
And it has a low service temperature, usually held to around 80 degrees C.
What acetal does well
Acetal is stiff, it barely absorbs water, it resists creep and it machines to tight tolerances that stay put. Against a clean steel counterface it has a low, consistent coefficient of friction and it does not gall.
That combination is what makes it the default for gears, bushings, cams and any part where a dimension is the whole point.
What acetal does badly
It is notch sensitive. Sharp internal corners and thin sections crack under shock. Against genuinely abrasive material it wears far faster than UHMW. And it is not the answer in strong acid or under long unprotected UV exposure.
Side by side
| Question | Acetal (POM) | UHMW-PE |
|---|---|---|
| Abrasion by bulk material | Moderate | Excellent |
| Impact and shock | Notch sensitive | Excellent |
| Creep under sustained load | Good resistance | Poor, deforms over time |
| Dimensional stability after machining | Good | Moves, hard to hold |
| Achievable machined tolerance | Tight | Loose |
| Stiffness | High | Low |
| Continuous service temperature | Around 90 degrees C | Around 80 degrees C |
| Coefficient of friction against steel | Low | Very low |
| Typical use | Gears, bushings, cams, precision parts | Chute liners, guides, wear strips, star wheels in abrasive lines |
How to choose in one pass
Ask what the part is really doing.
If it is holding a dimension, acetal. Gears, cams, bearing bores, spacers, anything with a fit.
If it is taking a beating, UHMW. Liners, guides, bumpers, anything that gets hit or scraped by bulk material.
If it is doing both, split the part. A common answer is an acetal body with a replaceable UHMW wear face, or a UHMW guide with an acetal bushing pressed into it.
A note on conveyor parts
Star wheels, chain guides and product handling parts often get specified in whichever material the plant last used. That is worth revisiting. A star wheel that indexes product to a position wants acetal, because the position is the function. A side guide that rubs against packaging all day wants UHMW, because nothing there is a dimension.
If you are not sure which side of that line your part sits on, put the service conditions on the RFQ and let the quoting shops comment. Send your RFQ and we match you with shops that machine both. Reply within 24 business hours.
Frequently asked questions
Which wears longer, acetal or UHMW?
It depends on what is wearing it. Against abrasive material such as grain, sand or glass cullet, UHMW lasts far longer. Against a clean steel shaft under load, acetal holds up better because it does not deform.
Can UHMW hold a tight tolerance?
Not really. UHMW is soft, it springs under clamping and it moves after machining. Plan on looser tolerances and avoid designing precision fits in it. If the part needs a bore within a few hundredths of a millimetre, it is an acetal part.
Is UHMW cheaper than acetal?
Per kilo it is usually cheaper, and it is much lighter, so a large part can cost noticeably less in stock. Machining time can go the other way, because soft material needs careful workholding and more finishing passes.
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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