Material guide
Delrin vs Acetal: Homopolymer vs Copolymer Explained
Delrin is acetal, but not all acetal is Delrin. Here's the real difference between acetal homopolymer and copolymer, what Delrin 150 and AF mean, and which to use for precision parts, food equipment and thick stock.
Delrin is acetal homopolymer; generic "acetal" is usually copolymer. Choose homopolymer (Delrin) when you want a bit more strength, stiffness and fatigue life. Choose copolymer for hot water, caustic or chlorinated washdowns, for food and medical parts, and for thick parts where center porosity would be a problem. Copolymer is usually also a little cheaper.
The short version
Acetal (polyoxymethylene, or POM) comes in two chemistries. Homopolymer (POM-H) is made of identical repeating units, which packs the molecules more tightly and makes it a bit stronger and stiffer. Delrin is the best-known brand. Copolymer (POM-C) has a small amount of a second unit built into the chain, which costs a little strength but makes it much more stable in hot water, steam and alkaline cleaners. On the shelf, natural white sheets of either look identical.
| Homopolymer (Delrin) | Copolymer acetal | |
|---|---|---|
| Tensile strength | ~10,000–11,000 psi | ~9,000–9,500 psi |
| Stiffness and hardness | Higher | Slightly lower |
| Creep and fatigue | Better | Good |
| Hot water, steam, caustic | Fair; degrades with long exposure | Better; more stable |
| Center porosity in thick stock | Can occur in standard grades | Generally free of it |
| Melting point | ~347°F (175°C) | ~330°F (165°C) |
| Max service temp | ~180°F (82°C) | ~180°F (82°C) |
| Relative cost | $$ | $–$$ |
Typical values for unfilled stock shapes. Confirm with the datasheet for your grade.
Strength and stiffness
Homopolymer's tighter molecular structure gives it roughly 10 to 15% more tensile strength and stiffness, higher surface hardness, and better resistance to creep and fatigue. For highly loaded gears, snap fits, springs and parts that flex millions of times, that margin can matter. For most bushings, rollers, fixtures and general machined parts, copolymer performs just as well.
Chemical resistance and washdown
Both handle oils, fuels, solvents and most neutral chemicals very well. The difference shows up with hot water, steam and alkaline cleaners: copolymer holds up noticeably better over time, which is why it's the more common choice on food, beverage and dairy equipment that sees daily caustic and hot-water washdowns. Neither handles strong acids, chlorine-heavy sanitizers or oxidizers well over the long term.
Center porosity
Thick standard homopolymer rod and plate can have a porous zone along the centerline. For a bushing or a bracket it rarely matters. For valve bodies, manifolds and fittings that must hold pressure, or for food and medical parts where pores can trap bacteria, it does. If the part is machined from the center of thick stock, specify copolymer or a porosity-free homopolymer grade.
Grade names you'll see
- Delrin 150: the standard homopolymer extrusion grade for rod, plate and tube.
- Delrin AF: homopolymer with PTFE fibers for lower friction and wear in bushings and bearings.
- Glass-filled acetal: stiffer and more dimensionally stable, but more abrasive to machine and less slippery.
- Copolymer brands: Celcon, Acetron GP, Tecaform AH, Ultraform and others, often sold simply as "acetal copolymer."
- POM-H / POM-C: shorthand for homopolymer and copolymer on prints and datasheets.
Machining
Both are among the easiest plastics to machine: they cut cleanly, hold tight tolerances (±0.001–0.002" is routine) and barely absorb moisture. Homopolymer can be slightly crisper to cut; copolymer is often preferred for thick parts because of porosity. Find CNC machine shops and turning shops that work with acetal below.
When to choose each
Choose homopolymer (Delrin) for
- Highly loaded gears, cams and snap fits
- Parts that flex or cycle millions of times
- Maximum stiffness and surface hardness
- Thin or small parts where porosity isn't a factor
- Delrin AF for dry-running bushings
Choose copolymer for
- Food, beverage and dairy equipment
- Hot water, steam and caustic washdown
- Thick parts machined from the center of stock
- Manifolds, valve parts and fluid handling
- General machined parts at a lower cost
Tip from the counter: a lot of prints say "Delrin" when the engineer just means "acetal." Before swapping either way, ask whether the part is loaded hard (stay with homopolymer) or sees washdown, pressure or thick sections (copolymer is usually the better pick).
Comparing acetal with other plastics? See Delrin vs UHMW and Delrin vs nylon.
Common questions
Is Delrin the same as acetal?
Delrin is a brand of acetal homopolymer (POM-H). "Acetal" on its own usually means acetal copolymer (POM-C), sold under names like Celcon, Acetron GP, Tecaform AH and Ultraform, or just "acetal copolymer." Both are polyoxymethylene and look and machine almost identically; the differences are in strength, porosity and chemical resistance.
Is Delrin 150 the same as acetal?
Delrin 150 is a specific Delrin homopolymer grade made for extruding rod, plate and tube. So it's acetal, but homopolymer acetal. If a print calls out Delrin 150 and you substitute copolymer, you're giving up a little strength and stiffness but gaining chemical resistance and usually freedom from center porosity. Check with the engineer before substituting.
Is acetal stronger than Delrin?
No. Delrin homopolymer is slightly stronger, stiffer and harder than acetal copolymer, with better creep and fatigue resistance. The difference is real but modest, roughly 10 to 15% on tensile strength and stiffness.
What is center porosity in Delrin?
Thick extruded homopolymer rod and plate can have a small porous zone along the centerline, a result of how the material cools. It's harmless for many parts, but it can cause leaks in fluid-handling parts, trap bacteria in food and medical parts, or show up as a defect after machining. Copolymer and porosity-free homopolymer grades avoid it.
What is Delrin AF?
Delrin AF is homopolymer acetal blended with PTFE (Teflon) fibers. It has lower friction and better wear than standard Delrin, so it's used for bushings, bearings and sliding parts that run dry. It costs more and is a bit weaker than standard Delrin.
Values in this guide are typical figures for common unfilled grades, for general comparison only. Properties vary by manufacturer, grade, filler, and shape. Before you specify, buy or machine a material for an application, check the manufacturer's datasheet and the material certifications for the exact grade you're getting, and confirm suitability with your supplier.
Who stocks and machines it
Distributors that stock these materials and shops that machine or fabricate them, from the Stock & Shape directory.
Acetal (Delrin)
- Cope Plastics – Hiawatha Hiawatha, IA
- Interstate Advanced Materials – Portland Portland, OR
- Laird Plastics – Orlando Orlando, FL
- Piedmont Plastics – Westchester Thornwood, NY
- Ehren-Haus Industries Fort Mill, SC
- J & N Metal Products Brazil, IN
- Maximum Industries Irving, TX
- Miles Products Brunswick, OH