Delrin vs Nylon 6/6

Delrin (POM-H) and Nylon 6/6 compared across seventeen properties, with the verdict on each — and the one property that decides most real choices.

Data verified 2026-09-29 · based on ASTM D6778-20

Quick Answer

Delrin (POM-H) vs Nylon 6/6 — Property Comparison

Nylon 6/6 values are dry as molded, which is the state the data sheets quote and not the state a part is in after a week in a normal room. Conditioned nylon has absorbed roughly 2.5% moisture, which plasticises it: tensile strength falls by about 40%, elongation and impact strength rise, and the part grows about 0.5–1.5% linearly. Every "nylon wins" verdict in this table should be read in that light — a conditioned nylon part is tougher and weaker than the figures shown.

The One Property That Decides Most Choices

Water absorption is the difference that matters. Delrin takes up 0.25% of its weight in water over 24 hours; nylon 6/6 takes up 1.2–1.5%, and reaches about 2.5% at equilibrium in ordinary indoor air. Five times as much water, and absorbed water pushes the polymer chains apart.

The result is a dimensional problem you cannot machine your way out of. A nylon part machined dry to a tight tolerance grows roughly 0.5–1.5% linearly as it equilibrates — half a millimetre to a millimetre and a half on a 100 mm dimension. It also changes shape unevenly: a thick section absorbs water more slowly than a thin one, so the part wargs as well as growing, and a reamed bore can become out of round. No amount of machining precision fixes this, because the movement happens after the machine.

For a bushing, a wear pad, a roller or a gear tooth this is usually acceptable — the part finds its own clearance and the toughness is worth the movement. For a bearing housing, a gauge, a valve seat, a fixture plate or anything that must fit another machined component to a tolerance, it is not. That distinction, more than any other, decides between the two materials in practice.

Where Nylon Genuinely Wins

Nylon is not the compromise choice. It wins on four counts, and on two of them it wins clearly.

Temperature. Nylon melts at 265 °C against Delrin's 175 °C, and its continuous rating is 105 °C against 85 °C. Counterintuitively, though, Delrin has the higher deflection temperature under load — 125 °C against nylon's 75 °C at 1.8 MPa — because Delrin retains stiffness closer to its melting point while nylon softens much earlier under load. So nylon is the material for a hot part with no load, and Delrin is the material for a loaded part that gets warm. Read the two rows together, not separately.

Toughness. Nylon's elongation at break is 40% against Delrin's 25%, and its impact strength holds up better at low temperature and under repeated loading. It is also notably better in fatigue — a nylon part will survive many more load cycles before cracking. For a snap fit, a latch, a wheel, or anything that takes shock, nylon is the better choice.

Abrasion. Nylon outlasts Delrin in sliding wear, particularly at high load and in dirty conditions where abrasive particles are present. Nylon also tolerates edge loading better because it deforms rather than chipping.

Cost. Nylon 6/6 is generally the cheaper of the two per kilogram, and its 20% lower density makes it cheaper again per part — which is why so much high-volume plastic hardware is nylon.

Where Delrin Wins

Dimensional stability, as covered above, is the headline. A Delrin part machined to size stays at that size through changes in humidity, which is why acetal is the default for precision machined plastic components and why it is used for gears that must mesh, cams with a timing relationship, and fixtures that hold other parts.

Machinability. Acetal produces a clean, continuous chip, takes a better surface finish and needs no coolant. Nylon is gummier, tends to melt and smear if the tool is dull, and leaves a burr that is difficult to remove cleanly. On a manual lathe, the difference is obvious.

Stiffness and hardness. Delrin's modulus is about 11% higher and its Rockwell M hardness nine points higher, which makes it the better material for a part that must resist deflection under load — a gear tooth, a cam follower, a structural spacer.

Friction consistency. Delrin's coefficient of friction is 0.20 and stays there; nylon's runs 0.25–0.40 and varies with moisture content and load. For anything where friction is a design input rather than an incidental, Delrin's predictability is worth more than nylon's lower minimum.

The decision rule that follows: if the part must fit something, choose Delrin. If the part must survive something, choose nylon.

Frequently Asked Questions

Is Delrin better than nylon?

Neither is better in general — they optimise different things. Delrin is stiffer, harder, far more dimensionally stable and cleaner to machine. Nylon is tougher, resists abrasion and fatigue better, tolerates higher temperatures and costs less per part. Choose Delrin when the part must hold a dimension and fit another component; choose nylon when it must absorb impact, resist wear, or run hot.

Why does nylon change size but Delrin does not?

Water absorption. Nylon 6/6 absorbs 1.2–1.5% of its weight in water over 24 hours and about 2.5% at equilibrium in indoor air; Delrin absorbs 0.25%. Absorbed water pushes the polymer chains apart, so a nylon part swells about 0.5–1.5% linearly between dry and conditioned — a millimetre on a 100 mm dimension. Delrin's movement is a fifth of that, which is why precision machined plastic parts are usually acetal.

Can I substitute nylon for Delrin in a machined part?

Only if the part's dimensions are not critical. The two are close in tensile strength and impact, so a bracket, pad or roller usually works in either. But if the part is a gear that must mesh, a bushing with a specified clearance, or a fixture that locates another component, the moisture-driven size change will show up — the nylon part will grow and tighten. Condition the nylon stock before final machining if you must make the substitution.

Which plastic is better for gears?

Both are used, and the choice follows the application. Delrin is the default for precision gears, small timing gears and anything where backlash must stay constant, because its dimensions do not move with humidity. Nylon is preferred for larger, higher-torque gears and for gears that see shock loading, because its fatigue and impact resistance are better — but the designer has to allow for the tooth thickness changing with moisture.

Related

• Delrin (POM-H) Properties
• Nylon 6/6 Properties
• Acetal Copolymer (POM-C) Properties
• PEEK Properties
• Plastic Machining Tolerances
• Plastic Service Temperature Chart

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

Data Sources

Cross-checked against:

• Both sides of the comparison taken from the same two data sheets cited on the individual material pages, so no figure is reconciled twice
• The moisture-conditioning effect on nylon checked against published conditioned-property data
• Deflection temperature and continuous rating checked against the UL relative thermal index for each material

Nylon 6/6 values are dry as molded. A conditioned nylon part has roughly 40% lower tensile strength, higher elongation and impact strength, and a linear dimension about 0.5–1.5% larger than the dry figure. Where a verdict in this table turns on a nylon advantage in strength, read it as applying to the dry state — in service the gap against Delrin narrows or reverses.

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