Acetal and nylon are the two most common choices for gears, bushings, clips and moving parts. They overlap a lot, but they behave very differently around moisture and heat.
Side by side
| Acetal (POM) | Nylon (PA) | |
|---|---|---|
| Moisture absorption | Very low | High (PA6, PA66) |
| Dimensional stability | Excellent | Changes as it absorbs water |
| Friction and wear | Low friction, smooth | Good; tougher against abrasion |
| Toughness | Good, stiff | Very tough, especially when conditioned |
| Heat resistance | Good | Higher, especially glass-filled PA66 |
| Fatigue (repeated flexing) | Excellent | Good |
| Chemical resistance | Good to fuels and solvents; poor to strong acids | Good to oils and fuels; poor to strong acids |
| UV resistance | Poor unless stabilized | Fair to poor unless stabilized |
| Glass-filled options | Limited | Very wide |
Typical, general comparisons. Individual grades vary; check the data sheet.
Choose Acetal (POM) when
- Tight tolerances in humid or wet conditions
- Low friction and smooth running (gears, slides, snap fits)
- Springy parts that flex repeatedly
Choose Nylon (PA) when
- Higher temperatures, or you need glass reinforcement
- Maximum toughness and impact
- The part can tolerate some dimensional change
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