POM (Acetal) vs PA66 (Nylon): Precision Component Material Selection
Published: 2026-06-02
The POM vs PA66 decision for precision mechanical components hinges on three factors: moisture environment, temperature requirement, and friction requirement. POM excels in: 1) humid/wet environments where it maintains dimensions (0.2% moisture...
The POM vs PA66 decision for precision mechanical components hinges on three factors: moisture environment, temperature requirement, and friction requirement. POM excels in: 1) humid/wet environments where it maintains dimensions (0.2% moisture absorption vs 2.5-3.0% for PA66), 2) low-friction bearing applications (coefficient of friction 0.2 vs 0.35 for PA66), and 3) applications requiring HDT above 100°C unfilled (POM HDT 110°C vs PA66 75°C). PA66 excels in: 1) high-temperature applications when glass-filled (PA66 30GF HDT 250°C vs POM 30GF HDT 160°C), 2) applications requiring toughness at low temperatures (PA66 maintains ductility to -40°C; POM becomes notch-sensitive below 0°C), and 3) applications requiring chemical bonding to TPEs (PA66 bonds; POM does not).
Cost comparison: POM homopolymer (Delrin 500P) ~$4-6/kg; PA66 unfilled ~$3-5/kg; PA66 30GF ~$4-7/kg. However, POM's higher density (1.41 vs 1.14 g/cm³ for PA66) means the per-part material cost difference is smaller than the per-kg price suggests — for a given part volume, POM weighs 24% more. For gears: POM is preferred for precision gears in humid environments (automotive window regulators, appliance timers); PA66 is preferred for gears requiring impact resistance (power tool gearboxes, where cold-start torque can shatter POM gears).
Comparison at a Glance
| Tensile Strength | POM: 70 MPa vs PA66: 80 MPa (dry) / 50 MPa (conditioned) |
|---|---|
| Melting Point | POM: 175°C vs PA66: 260°C |
| Shrinkage Rate | POM: 2.0% vs PA66: 1.5% |
| Flexural Modulus | POM: 2.8 GPa vs PA66: 2.8 GPa (dry) |
| Hdt | POM: 110°C vs PA66: 75°C (unfilled) |
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Delrin vs Zytel | |
| Hostaform vs Ultramid |
Frequently Asked Questions
Why do POM gears sometimes fail suddenly in cold weather?
POM undergoes a ductile-to-brittle transition below 0°C — impact strength drops by 60-80%. A POM gear that functions reliably at room temperature can shatter under cold-start torque at -20°C. PA66 does not exhibit this transition and retains ductility to -40°C, making it preferred for outdoor and cold-climate gear applications.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org