What Is the Difference Between Acetal and Delrin? A Practical Guide for Engineers and Buyers

2026.02.23 06:21

When I first started sourcing engineering plastics for CNC machining projects, I kept running into the same question: what’s the real difference between acetal and Delrin? Suppliers used the terms almost interchangeably, and that made it difficult to choose the right material for precision components.

If you’ve ever searched for acetal vs delrin, you probably noticed the same confusion. In this guide, I’ll break it down in simple terms, based on practical experience, so you can confidently decide which material fits your application.

Understanding Acetal: The Basics

Acetal is a thermoplastic polymer also known as polyoxymethylene (POM). It’s widely used in engineering and industrial applications thanks to its excellent dimensional stability, low friction, and high strength.

From my experience working with machine shops, acetal is often chosen for:

Gears

Bushings

Bearings

Rollers

Precision mechanical parts

It machines cleanly, holds tight tolerances well, and resists moisture better than many other plastics. That makes it ideal for both dry and slightly wet environments.

However, there’s an important distinction within acetal itself.

What Is Delrin?

Delrin is actually a brand name. It’s a homopolymer version of acetal originally developed and trademarked by DuPont. While all Delrin is acetal, not all acetal is Delrin.

That’s where much of the confusion around acetal vs delrin begins.

There are two main types of acetal:

Acetal Homopolymer (e.g., Delrin)

Acetal Copolymer

The difference lies in their molecular structure, which directly impacts performance characteristics.

Acetal Homopolymer vs Copolymer

When I’m comparing materials for a project, I focus on performance requirements first. Here’s how they typically differ:

1. Strength and Stiffness

Homopolymer acetal (like Delrin) generally offers:

Slightly higher tensile strength

Higher stiffness

Better fatigue resistance

If I’m designing parts that will handle repeated mechanical stress—like snap-fit components or small gears—I often lean toward homopolymer.

2. Chemical and Thermal Resistance

Copolymer acetal typically provides:

Better resistance to chemicals

Improved resistance to hot water

Lower centerline porosity

In humid environments or where chemical exposure is a factor, copolymer can sometimes outperform homopolymer.

3. Surface Finish and Machining

From a machining perspective, both materials perform well. However:

Homopolymer often gives a slightly smoother surface finish.

Copolymer tends to have more consistent internal structure.

If aesthetics and surface quality matter (for example, visible consumer components), that small difference may influence your decision.

Why the Confusion Around Acetal vs Delrin?

In practical purchasing situations, suppliers may list “acetal” without specifying whether it’s homopolymer or copolymer. Meanwhile, some buyers use “Delrin” as a generic term for all acetal materials.

This overlap creates misunderstanding, especially for new engineers or procurement teams.

The key takeaway I’ve learned is simple:

Delrin = acetal homopolymer (brand-specific)

Acetal = general category (includes homopolymer and copolymer)

Knowing that distinction makes sourcing much easier.

Performance Comparison Table (Simplified)

Here’s a quick summary I often use when deciding:

Property Homopolymer (Delrin) Copolymer Acetal

Strength Slightly Higher Slightly Lower

Stiffness Higher Moderate

Chemical Resistance Good Very Good

Moisture Resistance Good Excellent

Cost Often Higher Often Slightly Lower

Of course, exact numbers depend on grade and manufacturer.

Applications: Which Should You Choose?

In my experience, the choice depends less on brand and more on application demands.

Choose Homopolymer (Delrin) When:

You need maximum mechanical strength

Parts are under repeated stress

You want superior fatigue resistance

Surface finish is critical

Choose Copolymer Acetal When:

Parts operate in moist or chemically exposed environments

Dimensional stability in wet conditions is essential

You want slightly better resistance to hydrolysis

Cost efficiency is a priority

Cost Considerations

Pricing can vary based on supply chain conditions, but generally:

Delrin (brand-name homopolymer) may carry a premium.

Generic copolymer acetal can be more budget-friendly.

For large production runs, even small price differences per sheet or rod can add up significantly. I always compare performance needs against long-term cost efficiency rather than focusing only on upfront pricing.

CNC Machining Perspective

As someone who frequently works with CNC shops, I can say both materials machine extremely well.

Key advantages include:

Minimal warping

Tight tolerances

Smooth cutting

Reduced tool wear

However, I’ve noticed that homopolymer sometimes produces slightly cleaner edges in high-speed machining. If your project involves intricate detailing, that could matter.

Still, both are considered premium engineering plastics compared to many alternatives like nylon or ABS.

Environmental and Safety Factors

Both acetal homopolymer and copolymer are generally safe and stable when used properly. They offer:

Good wear resistance

Long service life

Low friction properties

That durability reduces the need for frequent replacements, which can be beneficial from both sustainability and cost perspectives.

Common Myths About Acetal and Delrin

Over time, I’ve heard a few misconceptions:

Myth 1: Delrin Is a Completely Different Material

Reality: It’s a type of acetal.

Myth 2: Copolymer Is Always Inferior

Reality: In certain chemical environments, copolymer can outperform homopolymer.

Myth 3: The Difference Is Huge

Reality: For many standard applications, the performance gap is relatively small.

Understanding these nuances prevents overpaying for brand name when it’s not necessary—or under-specifying material when strength really matters.

How I Decide Between Acetal and Delrin

When I evaluate a project, I ask myself:

Will the part face heavy mechanical stress?

Is it exposed to moisture or chemicals?

Are tight tolerances critical?

Is cost sensitivity a factor?

If strength and fatigue resistance are top priorities, I lean toward homopolymer. If chemical stability or moisture exposure is the bigger concern, copolymer often makes more sense.

The real solution isn’t choosing sides in the acetal vs delrin debate—it’s matching material properties to real-world performance needs.

Final Thoughts

Choosing between acetal and Delrin doesn’t have to be complicated. Once you understand that Delrin is simply a branded homopolymer version of acetal, the comparison becomes much clearer.

In practical terms:

Both materials are strong, machinable, and reliable.

The differences are technical but important for specific applications.

The right choice depends on performance requirements—not just brand recognition.

If you’re designing mechanical parts, sourcing materials for CNC machining, or evaluating plastic options for industrial components, taking the time to understand these distinctions can save money, improve durability, and prevent costly redesigns.