Acetal vs. Delrin: What’s the Difference?

Are you trying to pick between acetal and Delrin for your next project? Many engineers and designers get confused about these materials. While they look similar, they have key differences that can make or break your project.

In this guide, we’ll break down everything you need to know about acetal and Delrin in plain language. You’ll learn what makes them different, when to use each one, and how to pick the right material for your needs.

What Are Acetal and Delrin?

Before diving into the differences, let’s understand what these materials actually are.

Acetal (POM Copolymer)

Acetal is a thermoplastic polymer made from alternating units of ethylene oxide. The technical name is polyoxymethylene (POM). The most common type of acetal is a copolymer version, sold under brand names like Hostaform® and Celcon®.

Think of acetal as a tough, slippery plastic that works well in many mechanical applications. It’s often used when you need something that:

• Resists chemicals
• Has good stability
• Can be easily machined
• Doesn’t absorb much moisture

Delrin® (POM Homopolymer)

Delrin is actually a brand name owned by DuPont. It’s a specific type of acetal—a homopolymer version. This means its molecular structure is more uniform and crystalline than regular acetal.

The main things to know about Delrin are:

• It’s stronger than standard acetal
• It has better fatigue resistance
• It can handle more mechanical stress
• It costs more than generic acetal

As our experts at division explain, “Delrin and acetal are often treated as interchangeable, but their different molecular structures create important performance differences.”

Key Differences Between Acetal and Delrin

Let’s break down the most important differences between these materials:

1. Chemical Structure

• Acetal (Copolymer): Made with both formaldehyde and other materials like ethylene oxide
• Delrin (Homopolymer): Made almost entirely from formaldehyde

This difference in chemical makeup leads to many of their other differences.

2. Property Comparison

Here’s a detailed breakdown of how these materials compare:

3. Tensile Strength and Performance

The numbers don’t lie when it comes to strength:

As you can see, Delrin has about 20% higher tensile strength, which makes it better for parts that need to handle high loads. This is why Delrin is often chosen for precision CNC machining applications where strength is critical.

When to Use Acetal vs. Delrin

Choosing between these materials depends on your specific needs. Let’s look at when each one shines:

Best Uses for Acetal Copolymer

Acetal works best when you need:

1. Chemical resistance: If your part will be exposed to acids, bases, or solvents, acetal is the better choice.
2. Long-term heat stability: For parts that will face moderate heat for long periods, acetal holds up better.
3. Cost-effective solutions: When budget matters and you need good performance at a lower price.
4. Medical applications: Many FDA-compliant grades are available, making it good for medical devices.
5. Easier processing: The wider processing window makes it easier to work with in manufacturing.

Our specialists in acetal CNC machining have found that “acetal copolymer provides better dimensional stability in large parts, making it ideal for complex housings and frames.”

Best Uses for Delrin

Delrin excels when you need:

1. Superior strength: For high-load applications where strength is critical.
2. Excellent fatigue resistance: Parts that will face repeated stress cycles.
3. Precision parts: When tight tolerances and minimal warping are required.
4. Wear resistance: For moving parts like gears and bearings that face constant friction.
5. High-performance applications: When you need the best mechanical properties and can pay more.

For these reasons, Delrin is often selected for CNC Delrin machining projects where precision and strength are paramount.

Real-World Applications

Let’s look at how these materials are used in different industries:

Industry Case Studies

Medical Industry Applications

In the medical field, the choice between acetal and Delrin can be critical:

• Acetal is often used for drug delivery systems, surgical instruments, and dialysis equipment due to its chemical resistance and FDA compliance.
• Delrin works better for orthopedic trial components, surgical guides, and high-load medical equipment that needs strength and durability.

Automotive Applications

Car manufacturers use both materials but in different ways:

• Acetal appears in fuel system components, window systems, and small interior parts where chemical resistance matters.
• Delrin is chosen for gears, bushings, and precision components in transmissions and engine systems where mechanical stress is high.

Selection Guide: How to Choose

Follow these five steps to pick the right material:

1. Assess Chemical Exposure

Key question: Will your part face acids, bases, or strong chemicals?

• If yes → Choose acetal copolymer
• If no → Either material may work

2. Consider Mechanical Loads

Key question: Will your part face high mechanical stress or repeated load cycles?

• If yes → Choose Delrin
• If no → Acetal copolymer will likely work fine

3. Check Temperature Requirements

Key question: What temperature range will your part experience?

• Long-term heat exposure → Choose acetal (better stability)
• Short-term heat spikes → Delrin can handle higher peaks

4. Think About Budget

Key question: Is cost a major factor in your project?

• If yes → Acetal copolymer is about 30% cheaper
• If no → Consider Delrin for better performance

5. Evaluate Manufacturing Needs

Key question: How complex is your part, and what tolerances do you need?

• Tight tolerances and high precision → Delrin (less warpage)
• Complex shapes with wider tolerances → Acetal might be easier to work with

Limitations to Be Aware Of

Both materials have weaknesses you should know about:

Acetal Limitations

• Not ideal for high-impact applications
• Can’t handle temperatures above 90°C for long periods
• Lower mechanical strength than Delrin
• Not recommended for structural parts under high load

Delrin Limitations

• Poor resistance to UV light and weathering
• Susceptible to damage from chlorine and strong acids
• More expensive than generic acetal
• Narrower processing window makes manufacturing more challenging

As experts in custom plastic CNC machining have found, “Delrin’s higher crystallinity that gives it strength also makes it more challenging to machine to tight tolerances without specialized equipment.”

Common Questions About Acetal and Delrin

Here are answers to questions people often ask:

Making Your Final Decision

To make your final choice between acetal and Delrin, follow this simple decision path:

1. If chemical resistance is your top priority → Choose acetal
2. If mechanical strength is most important → Choose Delrin
3. If cost is your main concern → Choose acetal
4. If precision and stability under load matter most → Choose Delrin

Remember that in many applications, both materials will work well. The differences become important in extreme conditions or specialized uses.

Conclusion

Acetal and Delrin are similar materials with important differences in performance. Delrin is a branded homopolymer acetal with superior strength and fatigue resistance, while generic acetal is usually a copolymer with better chemical resistance and heat stability.

For the best results in your project:

• Choose Delrin when mechanical performance is critical
• Pick acetal when chemical resistance or cost matters more
• Consider working with specialists in plastic CNC machining who understand these materials’ unique properties

By understanding these differences, you can select the right material for your specific application needs. Whether you’re designing medical devices, automotive parts, or industrial components, choosing correctly between acetal and Delrin can make a significant difference in your product’s performance and lifespan.