Acetal vs. Delrin: What's the Difference and Which Should You Choose?

Quick answer: Delrin® (POM-H) is stronger and stiffer — better for gears, snap-fits, and high-load parts. Acetal copolymer (POM-C) resists chemicals and hot water better, costs less, and is the safer choice for hydraulic/pneumatic parts and large or thick components. Most general-purpose parts work fine with either.

When engineers and buyers start sourcing acetal plastic stock, one question comes up constantly: Is Delrin the same as Acetal? Are they interchangeable?

The short answer: they're related, but not the same. Here's what actually matters when you're choosing between the two.

What Are We Actually Talking About?

Acetal is the common name for Polyoxymethylene (POM) — a family of engineering thermoplastics known for high stiffness, low friction, and excellent dimensional stability.

Delrin® is a brand name owned by DuPont (now Celanese) for their specific grade of Homopolymer Acetal (POM-H). Most standard acetal on the market is Copolymer Acetal (POM-C) — a different molecular structure with different performance characteristics.

The Core Difference: Molecular Structure

POM-H (Delrin) is made from pure formaldehyde, resulting in a highly uniform, tightly packed polymer chain. This gives it higher tensile strength and rigidity.

POM-C is made by copolymerizing trioxane with a small amount of comonomer. This breaks up the chain uniformity slightly, which reduces peak mechanical strength — but dramatically improves thermal stability, chemical resistance, and processing consistency.

Neither is universally better. The right choice depends entirely on your application.

Performance Comparison

Three Things That Matter Most in Precision Machining

1. Centerline Porosity

This is the one most people don't talk about until it causes a problem.

When large-diameter POM-H rods or thick sheets are extruded, the outer layers cool faster than the core. Because homopolymer acetal has a higher crystalline shrinkage rate, microscopic voids form along the center axis as the core contracts.

For most structural applications, this is invisible and irrelevant. But if you're machining a manifold, a valve body, or any component that needs to hold pressure or seal fluid — centerline porosity can cause leaks, thread failures, and rejected parts.

POM-C has a uniform, non-porous cross-section throughout. For pneumatic and hydraulic components, it's the safer choice.

2. Dimensional Stability After Machining

POM-H has higher internal stresses from its crystalline structure. After heavy machining — especially on thin-walled or asymmetrical parts — it can warp slightly as internal stresses redistribute.

POM-C holds its dimensions more predictably after machining. For tight-tolerance parts with complex geometries, this matters.

3. Chemical and Thermal Environment

POM-H degrades in strong alkaline environments and prolonged hot water exposure. If your parts will be sterilized, cleaned with alkaline agents, or used in wet chemical environments — POM-C is the right call.

When to Use Each

Use POM-H (Delrin) for:

- High-load gears and pinions

- Spring-loaded snap-fit components

- High-frequency rollers and bushings where surface hardness matters

Use POM-C for:

- Hydraulic and pneumatic manifolds

- Medical device parts requiring sterilization

- Semiconductor equipment exposed to alkaline cleaning fluids

- Large flat plates where warping must be avoided

A Note on Cost

Delrin stock typically runs 15–30% higher than standard POM-C. Over-specifying to Delrin when POM-C would perform better — and cost less — is a common and avoidable procurement mistake.

If you're working on a custom component and need help deciding between POM-C and Delrin, feel free to reach out. Tell us about your application and we'll point you in the right direction.

What‘s App / E-mail