The short answer
Acetal homopolymer is a little stiffer, stronger and harder, and is often chosen for gears and highly loaded parts. Acetal copolymer is more stable in hot water, chemicals and the molding barrel, and easier to process. For most general parts either works.
Acetal (POM) is the go-to resin for precision mechanical parts: low friction, stable dimensions and good wear. It comes in two families, and the choice affects strength, chemical resistance and how forgiving the material is in the press.
Side by side
| Property | Homopolymer | Copolymer |
|---|---|---|
| Structure | Single repeating unit | Small share of a second unit for stability |
| Stiffness and strength | Higher | Slightly lower |
| Hardness and creep resistance | Higher | Slightly lower |
| Fatigue resistance | Higher | Good |
| Hot water and alkalis | Fair | Better |
| Thermal stability in the barrel | Narrower window | More forgiving |
| Melting point | ~175°C | ~165°C |
| Mold shrinkage | ~1.9–2.3% | ~1.8–2.2% |
| Typical uses | Gears, high-load snap fits, fasteners | Plumbing, food equipment, pump parts, clips |
Typical values for general-purpose, unfilled grades. Individual grades vary; check the data sheet.
Choose homopolymer when
- Gears and parts under steady load
- Snap fits and springs that need high stiffness and fatigue life
- Maximum hardness and creep resistance matter
Choose copolymer when
- Hot water, steam or cleaning chemicals are involved
- Long barrel residence or thick parts make processing tricky
- Plumbing, food equipment and pump parts
Processing notes
- Keep melt temperature and residence time within the data sheet; overheated acetal releases formaldehyde.
- Homopolymer is less tolerant of long residence times than copolymer.
- Never run acetal and PVC through the same barrel without a full purge; the combination can release corrosive gas.
- Most standard grades need little or no drying; toughened grades usually do. See the drying chart.
Grades we source
We source acetal homopolymer and copolymer, including lubricated, toughened and glass-filled grades, from one gaylord up, with a COA on every lot, tested to ASTM or ISO methods. See acetal (POM) and acetal vs. nylon.
Common questions
What is the difference between acetal homopolymer and copolymer?
Homopolymer is made of one repeating unit and is slightly stiffer, stronger and harder. Copolymer includes a small share of a second unit that makes it more stable in hot water, chemicals and long melt residence.
Which acetal is stronger?
Homopolymer, by a modest margin in stiffness, tensile strength and fatigue. It is often chosen for gears and highly loaded snap fits.
Is copolymer acetal better for hot water and chemicals?
Yes. Copolymer resists hot water, steam and strong alkalis better and is less prone to degrading when it sits in the barrel. It is often chosen for plumbing, food equipment and parts that see cleaning chemicals.
Do the two process differently?
Homopolymer has a narrower processing window and degrades faster if it overheats or sits in the barrel too long. Copolymer is more forgiving. Never mix acetal with PVC in the same barrel; the combination can release corrosive gas.
Can I swap homopolymer for copolymer?
Often, with checks. Expect slightly lower stiffness and a small shrinkage difference going to copolymer. Measure first parts and requalify where approvals are tied to the grade.
Tell us the acetal grade you run now
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province