Delrin vs Nylon
Delrin (acetal homopolymer, POM) and nylon 6/6 (polyamide) are the two default machinable engineering plastics for gears, bushings, wear pads and fixtures. Delrin is stiff, low-friction and dimensionally stable because it absorbs very little water. Nylon is tougher and more abrasion resistant but picks up 2 to 3% moisture at equilibrium, which swells it, softens it and shifts tolerances.
Pick Delrin when the part must hold size, run against metal with low friction, or machine to a tight tolerance. Pick nylon when the part takes impact or abrasive loading, runs at slightly higher temperature, or is a rope sheave, roller or wear strip where a little dimensional drift does not matter.
| Property | Delrin (acetal) | Nylon 6/6 |
|---|---|---|
| Polymer | Acetal homopolymer (POM-H) | Polyamide 6/6 (PA66) |
| Density | 1.41 g/cm³ | 1.14 g/cm³ |
| Tensile strength (dry, molded) | ~69 MPa (10 ksi) | ~83 MPa (12 ksi) dry; ~55 MPa conditioned |
| Flexural modulus (dry) | ~2.8 GPa (410 ksi) | ~2.8 GPa dry; ~1.2 GPa conditioned |
| Elongation | 25-40% | 30-60% dry; higher conditioned |
| Water absorption (24 h) | ~0.25% | ~1.2% (2.5-3% at saturation) |
| Melting point | ~175 °C (347 °F) | ~255 °C (491 °F) |
| Max continuous service | ~85 °C (185 °F) | ~95 °C (200 °F) |
| Coefficient of friction vs steel | Low (~0.2) | Moderate (~0.25-0.4) |
| Machinability | Excellent | Good; stringy chips, deflects |
| Typical uses | Gears, bushings, precision fixtures, valve bodies | Sheaves, rollers, wear strips, impact parts |
Typical values for the stated conditions. Confirm against the mill certificate and your spec.
Need a Delrin (acetal) or Nylon 6/6 part made?
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Decision matrix
A check marks the side with the edge on that dimension.
| Dimension | Delrin (acetal) | Nylon 6/6 |
|---|---|---|
| Machining | ✓ Excellent; crisp chips, holds ±0.05 mm | Good; stringy chips, springs away from the tool, tolerances open up |
| Welding | Poor; difficult to hot-plate or solvent bond | ✓ Fair; hot-plate and ultrasonic welds possible |
| Forming | Poor; machined or molded, not formed | Poor; machined or molded |
| Strength | Stiff, creep resistant, notch sensitive | Higher tensile dry, tougher, but softens with moisture |
| Corrosion resistance | ✓ Good with solvents, fuels; attacked by strong acids and chlorine | Good with oils, solvents; attacked by strong acids, swells in water |
| Finishing | Machined finish is the finish; paints poorly | ✓ Machined finish; dyes and paints better than acetal |
| Material cost | Baseline engineering plastic | Similar; cast nylon 6 cheaper in large shapes |
| Availability | Rod, plate, sheet everywhere | Rod, plate, tube; cast nylon in big sections |
Choose Delrin (acetal) when
- Precision parts that must hold tolerance across humidity changes
- Gears, bushings and slides running against metal with low friction and no lubricant
- Fuel, solvent or water contact where nylon would swell
- The part is machined to a fine finish and a tight fit
Choose Nylon 6/6 when
- Impact and abrasive loading: sheaves, rollers, guide blocks, hammer heads
- Sustained service a little hotter than acetal tolerates
- Large machined shapes where cast nylon is cheaper and tougher
- Slight dimensional drift is acceptable and toughness is not negotiable
Frequently asked questions
- Is Delrin stronger than nylon?
- Dry nylon 6/6 has a higher tensile strength, about 83 MPa against 69 MPa for Delrin. Conditioned to normal room humidity, nylon drops to roughly 55 MPa and loses about half its stiffness, so in real service Delrin is usually the stiffer, more predictable material.
- Which machines better, Delrin or nylon?
- Delrin. It cuts like a soft metal with short chips and holds tight tolerances. Nylon produces long stringy chips, deflects under the tool and grows or shrinks with humidity, so its practical tolerance is looser.
- Does Delrin absorb water?
- Very little, about 0.25% in 24 hours and under 1% saturated, which is why it keeps its size and stiffness in wet service. Nylon 6/6 absorbs 2.5 to 3% at saturation and swells measurably.
- Which is better for gears?
- Delrin for precision gears with a metal mate and no lubrication: lower friction, better tooth accuracy and stable backlash. Nylon for shock-loaded or abrasive gears where a little backlash drift is acceptable and toughness matters more.
