Nylon vs Acetal: Choosing the Right Engineering Plastic

Nylon and acetal (also known as Delrin or POM) are the workhorses of precision-machined plastic components. Both are semi-crystalline thermoplastics with good wear resistance, moderate chemical resistance, and a sharp melting point — but they are not interchangeable. Choosing the wrong one can lead to dimensional creep, moisture-related failure, or premature wear.

At P&M Plastics, our CNC team machines components from both materials daily. Here's what you need to know.

Moisture Absorption — The Critical Difference

This is the most important distinction between the two materials. Nylon absorbs 3 to 9 times more moisture than acetal. Nylon 6/6 can reach 7% moisture saturation, which causes the material to swell and lose dimensional accuracy. In precision-fit applications — bushings, gears, slide bearings — this dimensional change can cause binding or failure.

Acetal absorbs very little moisture and maintains its dimensions reliably across a wide range of humidity conditions. For any application where dimensional stability is critical, or where the part will be exposed to water, acetal is almost always the correct choice.

Tensile vs Compressive Strength

Nylon has higher tensile strength. Nylon 6/6 can reach tensile strengths of 70–85 MPa, compared to acetal's 60–70 MPa. For parts that need to resist being pulled or stretched — structural brackets, snap-fit clips, cable ties — nylon is more resilient.

Acetal has better compressive strength. For components under sustained compressive load — support pads, thrust washers, cam followers — acetal resists creep (slow deformation under load) better than nylon.

Friction and Wear

Both materials are used extensively for low-friction applications, but acetal has a lower coefficient of friction against steel — typically 0.20–0.35 for acetal versus 0.30–0.45 for unfilled nylon. In dry sliding applications, acetal will generate less heat and wear more slowly.

In lubricated applications, the gap narrows. Nylon can self-lubricate when moisture is present, which is why it's used in some water-exposed bearing applications.

Temperature Resistance

Nylon handles higher temperatures. Nylon 6/6 has a continuous service temperature of around 120°C, versus acetal's 90°C. For components near heat sources, engines, or industrial ovens, nylon is the better choice. Acetal begins to soften and lose stiffness above 90°C.

Machinability

Acetal is the most machinable plastic. It cuts cleanly, produces tight tolerances, generates minimal burrs, and holds dimensions extremely well during and after machining. It's the first choice in our CNC workshop whenever tight tolerances are required.

Nylon is also readily machinable, but its tendency to absorb moisture (including coolant) can cause dimensional changes after machining. Parts should be machined to their final environment when possible.

Chemical Resistance

Both materials have good chemical resistance to oils, greases, and common solvents. Acetal is better in acidic environments, while nylon has better resistance to bases and some organic chemicals. Neither handles strong oxidising acids well.

Cost

Acetal shapes are typically around 25% less expensive than nylon 6/6 and about 25% more expensive than nylon 6. For most applications, acetal offers excellent value given its superior dimensional stability and machinability.

Appearance

A quick visual check: acetal is shiny and smooth (typically white or black), while nylon has a more matte, slightly textured appearance. This can be useful for quick identification on the shop floor.

Which Should You Choose?

Choose Acetal when you need:

Dimensional stability in humid environments • Low friction in dry sliding applications • Tight machined tolerances • Compressive strength under sustained load • Gears, bushings, slide rails, cam followers, valve components

Choose Nylon when you need:

Higher tensile strength • Elevated temperature resistance • Flexibility and impact toughness • Structural brackets, snap-fits, under-bonnet components, rope sheaves

CNC Machining at P&M Plastics

P&M Plastics stocks nylon and acetal in sheet, rod, and tube form and machines custom components to your drawings. Browse our materials at /materials/nylon-plastic and /materials/acetal-sheet-rod, or compare properties side by side at /materials/compare. Contact us on 07 5535 7544 or email for a machining quote.