POM / Delrin vs Nylon 66 (PA66)
POM (Delrin) and Nylon 66 (PA66) are the two workhorse engineering plastics for gears, bushings, and precision machined parts. Delrin offers higher stiffness, excellent dimensional stability, and very low moisture absorption, making it the default for tight-tolerance parts. Nylon 66 is tougher, has higher tensile strength (~83 vs ~70 MPa) and a higher service temperature, but it absorbs moisture, which swells parts and shifts dimensions.
The verdict
Choose POM/Delrin for precision parts where dimensional stability, low friction, and low moisture pickup are critical. Choose Nylon 66 when you need higher toughness, impact resistance, higher service temperature, or better wear in lubricated conditions — and can manage its moisture absorption.
Side-by-side data
| Property | POM / Delrin | Nylon 66 (PA66) |
|---|---|---|
| Category | Engineering Plastic | Engineering Plastic |
| Density (g/cm³) | 1.41 | 1.14 |
| Tensile strength (MPa) | 70 | 83 |
| Yield strength (MPa) | 65 | 80 |
| Elongation (%) | 40 | 60 |
| Hardness | R120 | R120 |
| Max service temp (°C) | 90 | 100 |
| Machinability | ●●●●● | ●●●●● |
| Corrosion resistance | ●●●●● | ●●●●● |
| Relative cost | ●●●●● | ●●●●● |
| Thermal cond. (W/m·K) | 0.31 | 0.25 |
| Typically used for | Precision low-friction machined parts | Gears, bushings & wear parts |
Which should you choose?
Choose POM/Delrin when…
- Dimensional stability is critical — Delrin absorbs little moisture and holds tolerances better than nylon
- You need higher rigidity and stiffness for precision gears, cams, and snap fits
- Low, consistent friction matters; Delrin machines (4.5/5) to a smooth, dimensionally stable surface
- The part runs in dry conditions where nylon's moisture-driven swelling would be a problem
- You need good fatigue resistance for repeated-flex mechanisms
- Tight machined tolerances must survive humidity changes
Choose Nylon 66 when…
- Toughness and impact resistance matter — PA66 has higher elongation (~60% vs ~40%) and tensile strength (~83 vs ~70 MPa)
- Service temperature is higher; nylon 66 handles ~100 C vs Delrin's ~90 C
- The bearing or gear runs with some lubrication, where nylon wears well
- Cost favors nylon (~1.5 vs Delrin ~2.0) at volume
- Moderate moisture absorption is acceptable or can be conditioned for
- You want a tougher, more forgiving material for shock-loaded wear parts
Key differences that matter
- Nylon 66 has higher tensile strength (~83 vs ~70 MPa) and elongation (~60% vs ~40%), so it is tougher and more impact-resistant
- Delrin's key advantage is dimensional stability — it absorbs far less moisture than nylon, holding tolerances in humid conditions
- Nylon 66 absorbs moisture, which swells parts and shifts dimensions; this must be designed around for precision work
- Delrin is more rigid and machines better (4.5 vs 3.5), favoring tight-tolerance precision parts
- Nylon 66 has a higher max service temperature (~100 C vs ~90 C)
- Both are excellent low-friction bearing and gear materials; choice hinges on stability vs toughness
- Delrin is denser (1.41 vs 1.14 g/cm3), so nylon parts are lighter for the same volume
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Open the Material SelectorGet a Quote →Frequently asked questions
Why does Delrin hold tolerances better than nylon?
Nylon 66 absorbs moisture from the air, which causes it to swell and grow dimensionally — a part machined dry can shift noticeably once conditioned. Delrin (POM) absorbs very little moisture, so its dimensions stay stable across humidity changes. That makes Delrin the preferred choice for precision gears and close-tolerance machined parts.
Which is tougher, Delrin or Nylon 66?
Nylon 66 is tougher. It has higher tensile strength (about 83 vs 70 MPa) and greater elongation (about 60% vs 40%), so it absorbs more impact before failing. Delrin is stiffer and more dimensionally stable but somewhat more notch-sensitive. For shock-loaded wear parts, nylon is generally the more forgiving option.
Can both be used for gears and bushings?
Yes — both are classic gear and bushing materials with low friction and good wear. Delrin suits dry-running precision gears needing dimensional stability. Nylon 66 suits tougher, sometimes-lubricated applications and runs slightly hotter (~100 C vs ~90 C). The decision depends on whether stability or toughness and temperature lead your requirements.
Does Delrin's higher density matter?
It can. Delrin is about 1.41 g/cm3 versus nylon 66's 1.14, so a Delrin part weighs roughly 24% more for the same geometry. In weight-sensitive assemblies that favors nylon, but for most precision mechanical parts the density difference is secondary to stability, stiffness, and moisture behavior.
Property values are typical/nominal figures for early-stage guidance only and vary by temper, grade, supplier and heat treatment. Confirm critical specifications against a certified datasheet or with an mfgiq engineer before production.