Short answer: Delrin is a type of acetal
Delrin is the trademarked acetal homopolymer (POM-H) originally developed by DuPont. “Acetal,” “POM” and “polyoxymethylene” are the names of the whole plastic family. When a supplier or datasheet says plain “acetal,” it almost always means the copolymer (POM-C).
The practical split: homopolymer is stiffer and stronger. Copolymer is more stable in hot water and chemicals, less prone to porosity in thick stock, and usually cheaper. Both machine very well on CNC equipment, so the choice comes down to the part’s load, environment and stock size.
Acetal, POM, Delrin: the names explained
One family, two chemistries
Homopolymer is built from a single repeating unit, so its chains pack tightly and it is more crystalline. Copolymer adds a small amount of comonomer along the chain. That breaks up the regular order, lowers crystallinity and makes the chain harder to attack with hot water or alkali. Both are semi-crystalline engineering plastics with low friction and good wear behavior.
Names you will see on a datasheet
- Delrin: the brand name for POM-H.
- Celcon, Hostaform, Duracon: trade names of copolymer grades from different resin makers.
- Polyacetal, polyoxymethylene, POM: generic family names covering both types.
A quote request that just says “acetal” leaves the chemistry open, which is why the callout section below matters.
Delrin vs acetal copolymer: side-by-side
| Property | Delrin (homopolymer, POM-H) | Acetal copolymer (POM-C) |
|---|---|---|
| Chemistry | Single repeating unit, higher crystallinity | Comonomer added, lower crystallinity |
| Strength and stiffness | Higher | Somewhat lower |
| Creep and fatigue resistance | Better under sustained or cyclic load | Good, but below homopolymer |
| Centerline porosity in thick stock | More likely | Low |
| Hot water, steam, chlorinated water | Weaker | Better |
| Alkali and general chemical resistance | Good | Better |
| Machinability | Excellent | Excellent |
| Cost | Higher | Generally lower |
| Lot-to-lot consistency | Single controlled brand | Varies by resin maker |
Values vary by grade, filler and stock form. Compare the current manufacturer datasheets for the exact grades before you commit a design.
Centerline porosity is the difference that matters most for machined parts. In extruded rod and plate, the outside cools first and the center sets last, which can leave tiny voids along the middle of the profile. A part turned or milled from the core of thick stock can expose them, which is a problem for sealing faces, pressure-bearing parts and thin walls near the center. Copolymer is the usual choice for large diameters and thick plate for this reason. Small-diameter bar and thin sections are much less exposed.
When Delrin is the better pick
- Gears, bearings and fasteners under sustained load, where stiffness and creep resistance keep the part in shape.
- Small or thin structural parts that need to resist deflection.
- Parts under repeated cyclic loading, where fatigue resistance counts.
- Programs where tight lot-to-lot consistency from a single branded grade is part of the requirement.
The trade-offs: possible porosity in thick stock, weaker performance in hot or chlorinated water and strong alkali, and a higher material price than copolymer.
When acetal copolymer is the better pick
- Wet, hot or chemically aggressive service, including cleaning chemicals and chlorinated water.
- Thick plate or large-diameter rod, where low porosity protects the finished part.
- Cost-sensitive parts where the last increment of stiffness is not needed.
- Parts that need a filled grade. Both families come in filled versions, so check the datasheet for the filler you want.
How to call it out on a drawing or RFQ
A material note that says only “acetal” or only “Delrin” forces the shop to guess. A clear callout avoids that:
- Write the chemistry. “POM-H (acetal homopolymer)” or “POM-C (acetal copolymer),” not “acetal” alone.
- Say whether the brand is mandatory. “Delrin 150 or equivalent” opens sourcing to equivalent homopolymer grades. “Delrin only” restricts it and can add cost and lead time, so use it only when the brand is a real requirement.
- State the stock form and size. Rod, plate or tube, plus diameter or thickness, so the porosity risk of thick sections is visible to everyone.
- Add grade or filler requirements. Natural, black, PTFE-filled or glass-filled.
- Request documents. Material certificates and inspection reports are available on request under our quality system, and you can see what a first-article inspection report contains before you ask for one.
- Describe the service conditions. Load, wear, temperature, water or chemical exposure, so the machinist can flag a mismatch before cutting.
Plastic dimensions move with temperature and moisture, so achievable tolerances depend on the material and the part’s geometry. Machining tolerances explains how to set them realistically. If the part is still being validated, a short prototype run lets you test the POM grade before you commit to volume.
Send a STEP file and a 2D drawing with the material callout through Contact Us, and we confirm the available POM grade when we quote your machined plastic parts.
Delrin vs nylon, PEEK and ABS: quick comparison
- Nylon: absorbs more moisture, so its dimensions drift with humidity. POM is steadier and has lower friction, while nylon can be tougher in impact-heavy uses.
- PEEK: handles far higher temperatures and harsher chemicals than POM, at a much higher material cost. Choose it when POM’s limits are the problem, not by default.
- ABS: cheaper and easy to form, but a weaker choice for wear surfaces and precision mechanical parts.
- Where POM sits: a stiff, low-friction, dimensionally stable plastic between commodity grades and high-performance polymers. That is why it is common for gears, bushings, guides and precision housings.
Whichever material you pick, the same callout rules apply. Name the grade, the stock form and the environment.
Have a POM part to machine? Upload your drawing with the material callout through Contact Us and we’ll come back with a quote and DFM feedback.
FAQ
Is Delrin the same as acetal?
Delrin is one type of acetal: a branded homopolymer. Not all acetal is Delrin.
Is acetal cheaper than Delrin?
Generally yes. Copolymer acetal usually costs less than branded Delrin homopolymer, though actual prices depend on grade, stock form and supplier.
Is acetal stronger than Delrin?
Not usually. Delrin homopolymer typically has higher strength, stiffness, and creep and fatigue resistance. Copolymer acetal does better in hot water and harsh chemical conditions.
What is another name for Delrin?
Delrin is the brand name for acetal homopolymer, also called POM-H, polyoxymethylene or polyacetal.
What are the disadvantages of Delrin material?
Possible centerline porosity in thick stock, weaker resistance to hot or chlorinated water and strong alkali, and a higher price than copolymer.
What is the difference between Delrin and POM-C?
Delrin is POM-H, the homopolymer. POM-C is the copolymer, which is more chemically stable, less porous in thick stock and usually cheaper.
Which should I put on my drawing: Delrin or acetal?
Specify the chemistry, POM-H or POM-C. Add “Delrin or equivalent” unless the Delrin brand itself is required.
How does Delrin compare with nylon?
POM is generally more dimensionally stable in humid conditions and has lower friction. Nylon can be tougher in some applications.
