Acetal vs Delrin: The Ultimate Engineer's Guide for Precision Parts

If you've ever found yourself searching for "acetal vs delrin" or "delrin vs acetal," you know how confusing the terminology can be. Are they the same thing? Is one better? The truth is, both acetal and delrin fall under the umbrella of POM (polyoxymethylene), a high-performance engineering thermoplastic. But the difference between acetal homopolymer vs copolymer is critical for your project's success.

Choosing incorrectly can impact everything from chemical compatibility and delrin temperature range to the hardness of delrin and overall part cost. This guide is designed to solve the POM puzzle once and for all, giving you a clear understanding of acetal plastic properties and delrin mechanical properties so you can make the most informed material selection for your precision parts.

Before diving into the comparison, it's essential to understand what each term means. People often use these names interchangeably, but there are important distinctions.

What is Polyoxymethylene (POM)?

Polyoxymethylene (POM), often called polyacetal, is the scientific name for a class of semi-crystalline thermoplastics known for their high strength, stiffness, and excellent dimensional stability. POM materials exhibit low friction and good wear resistance, making them ideal for precision parts that require a metal-like performance but with less weight. When people discuss pom vs delrin, they are often comparing the general material family to a specific brand name within it.

What is Acetal? (POM Copolymer)

Acetal, most commonly referring to acetal copolymer (POM-C), is an engineering plastic where the polymer chain is made with a second, different monomer inserted periodically. This structure disrupts the crystal structure, giving acetal copolymer enhanced long-term chemical resistance, especially against alkalis and hot water. It's known for its excellent balance of properties, low porosity, and is often a more cost-effective choice for a wide range of applications. The term "acetal plastic" broadly encompasses these copolymer materials.

What is Delrin? (POM Homopolymer)

Delrin is the famous brand name for acetal homopolymer (POM-H) developed by DuPont. The delrin polymer has a uniform molecular structure consisting of repeating CH₂O units, which results in a higher degree of crystallinity than the copolymer. This translates to superior delrin mechanical properties, including higher tensile strength, stiffness, and incredible fatigue endurance. So, when you see delrin acetal, it specifically refers to this homopolymer type. It's the go-to material for high-performance gears, bearings, and components under continuous stress.

Table: Acetal vs Delrin - The Basics

Now, let's get into the direct, side-by-side comparison of acetal copolymer vs delrin. This is where the critical differences for engineering decisions become clear.

Mechanical Properties: Strength, Stiffness, and Fatigue

When it comes to raw mechanical performance, Delrin homopolymer generally has the edge. It boasts higher tensile strength and impact resistance compared to acetal copolymer. Most notably, Delrin has a dramatically higher fatigue endurance limit, making it the undisputed choice for living hinges, snap-fit latches, and gears that undergo constant cyclic loading. The hardness of Delrin (typically Rockwell M94 for Delrin 150) is also higher than standard acetal copolymer, contributing to its excellent wear characteristics.

Acetal copolymer, while not as strong as Delrin, still offers very good mechanical properties that are sufficient for many applications. Its advantage lies in its ability to maintain these properties over long periods when exposed to high temperatures.

Thermal Properties: Melting Point and Temperature Range

Both materials have similar melting points—around 175°C (347°F). However, their performance over time differs.

The acetal temperature range for continuous use is typically up to 90–100°C (194–212°F). Acetal copolymer generally demonstrates better long-term stability against thermal degradation and oxidation when exposed to high temperatures for extended periods.

Delrin can withstand higher intermittent temperatures (up to 120°C) but may degrade with prolonged exposure at these highs. Its heat deflection temperature is around 115°C at 1.8 MPa, indicating good stability under load.

Chemical Resistance and Moisture Absorption

This is a key differentiator. Acetal copolymer offers superior resistance to strong bases (alkalis), hot water, and a wider pH range. It is less prone to hydrolysis, making it ideal for plumbing components and parts exposed to caustic environments.

While Delrin has good resistance to hydrocarbons, solvents, and neutral chemicals, it is more susceptible to attack by strong acids and oxidizing agents.

A critical similarity is that both materials have very low water absorption (about 0.2% for Delrin), which is why they maintain superb dimensional stability in humid environments.

Table: Key Property Comparison: Acetal vs Delrin

So, which one should you choose for your project? The answer depends entirely on your application's demands. Here’s a practical guide to help you decide.

Choose Delrin Homopolymer When...

• You need the highest possible mechanical strength, stiffness, and fatigue resistance. This makes it ideal for high-performance gears, bearings, springs, and snap-fit connectors that experience continuous stress.
• Excellent impact resistance is critical, even at lower temperatures. Delrin's toughness remains consistent from -40°C to 90°C.
• You are molding complex, thin-walled parts that require high flowability during injection molding.

Choose Acetal Copolymer When...

• Chemical resistance to alkalis, hot water, or oxidizing agents is a primary concern. It is the preferred material for plumbing fittings, chemical handling components, and fuel sender units.
• You are manufacturing parts with thick cross-sections, as it is less prone to centerline porosity than Delrin.
• Your project requires a great balance of properties at a more budget-friendly cost.
• You need good overall performance with better long-term thermal aging resistance.

Common Grades and Modifications

Both materials come in various grades to meet specific needs. For Delrin, common grades include:

• Delrin 100: A standard general-purpose grade.
• Delrin 150: Known for high impact resistance and low friction, ideal for gears and bushings.
• Delrin AF (PTFE-filled): Infused with Teflon® fibers for very low friction and high wear resistance—perfect for bearings.
• ESD Delrin: Formulated for static control in electronics manufacturing environments.

Acetal copolymers are also available in glass-filled or lubricated versions to enhance specific properties like stiffness or wear. Glass-filled acetal can see significant increases in strength and stiffness because the copolymer structure bonds well with the glass fibers.

How Does It Compare to Nylon and UHMW?

• Delrin vs Nylon: Nylon is generally stronger and has better impact resistance, but it absorbs significant moisture, which changes its dimensions and properties. Delrin is superior for applications requiring low friction, high wear resistance, and precise dimensional stability without moisture absorption.
• Delrin vs UHMW: UHMW (Ultra-High Molecular Weight Polyethylene) is much softer and has exceptional impact and abrasion resistance. However, Delrin is far stiffer, has a higher melting point, and can be machined to much tighter tolerances. UHMW is better for impact-absorbing liners, while Delrin is for precision mechanical parts like gears and bearings.

Machining Tips for Acetal and Delrin

Both acetal machining and machining Delrin are straightforward processes, making them favorites for CNC machining. They are considered free-machining plastics. For best results:

• Use sharp, positive-rake tools (HSS or carbide) to achieve a smooth finish.
• Both materials can produce stringy chips. Use compressed air or proper chip breakers to manage them effectively.
• Due to their low thermal conductivity, use adequate coolant or an air jet to prevent heat buildup during machining.
• For the best finish, some machinists recommend keeping a set of end mills dedicated to plastics to avoid contamination from metal chips.

Conclusion: Making the Informed Choice

The "acetal vs delrin" debate doesn't have a single winner—it has a right choice for your specific project.

• If your priority is top-tier mechanical strength, fatigue resistance, and stiffness for high-stress components like gears and snap-fits, Delrin homopolymer is the ideal candidate.
• If you need excellent chemical resistance, better performance in thick sections, and a cost-effective solution for applications like plumbing or chemical handling, acetal copolymer is the superior choice.

Ready to Bring Your Project to Life with Clarwe.com?

Understanding the difference between acetal and delrin is the first step. The next is partnering with a manufacturing expert who can guide you from design to finished part.

At Clarwe, we are specialists in acetal machining and producing high-performance parts from both delrin plastic and acetal plastic. Our engineering team provides free Design for Manufacturability (DFM) analysis to ensure your design is optimized for cost, performance, and lead time.

Upload your CAD file to Clarwe today for an online quote and see how our expertise can make your project a success.