Nylon vs. Delrin: In‑Depth Technical Comparison for High‑Wear Applications
Molecular structure, mechanical behaviour, environmental resistance, and selection criteria for two engineering thermoplastics
Both nylon (polyamide, PA) and Delrin (acetal homopolymer, POM) are widely used in injection moulding and CNC machining. However, their differences in molecular architecture lead to significantly different performance in wear, moisture, temperature, and long‑term creep. This guide provides a technical deep dive to support material selection.
For basic property tables, refer to our Materials Comparison Guide.
1. Molecular Structure and Crystallinity
| Property | Nylon (PA 6, PA 66) | Delrin (POM) |
|---|---|---|
| Polymer type | Semi‑crystalline polyamide | Semi‑crystalline acetal homopolymer |
| Repeating unit | –[NH–(CH₂)ₙ–CO]– | –[CH₂–O]– |
| Hydrogen bonding | Strong interchain H‑bonds (amide groups) | No H‑bonds; polar but flexible ether linkages |
| Typical crystallinity | 30–45% (PA 66) | 60–80% |
| Glass transition (Tg) | ~50–60°C (dry) | ~ –60°C (very low) |
| Melting point (Tm) | PA 66: ~260°C; PA 6: ~220°C | ~175–180°C |
Key insight: POM’s higher crystallinity and lack of moisture‑sensitive H‑bonds give it superior dimensional stability and lower creep under humidity. Nylon’s H‑bonding provides higher dry‑state strength and toughness but makes it hygroscopic.
2. Mechanical Properties: Strength, Stiffness, and Creep
| Property (dry, 23°C) | Nylon 66 | Nylon 6 | Delrin (POM) |
|---|---|---|---|
| Tensile strength (MPa) | 70–85 | 60–75 | 60–70 |
| Tensile modulus (GPa) | 2.5–3.5 | 2.0–3.0 | 2.8–3.4 |
| Elongation at break (%) | 20–50 | 30–100 | 10–40 |
| Notched Izod impact (kJ/m²) | 4–8 | 5–12 | 6–9 |
| Creep modulus (1000h, 23°C, 10 MPa) – dry | ~1.5 GPa | ~1.4 GPa | ~2.2 GPa |
| Creep modulus (1000h, 23°C, 10 MPa) – wet (2.5% moisture) | ~0.8 GPa | ~0.7 GPa | ~2.1 GPa (nearly unchanged) |
Creep resistance: POM maintains stiffness under long‑term load, especially in humid environments. Nylon’s creep performance degrades significantly with moisture absorption.
Glass‑filled variants (e.g. 30% GF) increase tensile modulus to 8–12 GPa for both materials, but POM remains less moisture‑sensitive.
3. Wear and Friction Mechanisms
| Property | Nylon | Delrin |
|---|---|---|
| Coefficient of friction (dry vs. steel) | 0.3–0.5 | 0.2–0.35 |
| Limiting PV (pressure × velocity) for unlubricated bearings (MPa·m/s) | ~0.1 | ~0.5–1.0 |
| Wear rate (mm³/Nm) against steel, dry | 10–30 × 10⁻⁶ | 1–5 × 10⁻⁶ |
| Abrasion resistance (Taber, CS‑17 wheel) | Moderate (80–120 mg/1000 cycles) | Excellent (30–50 mg/1000 cycles) |
Why POM wears less: POM forms a smooth transfer film on counterfaces due to its low surface energy and highly crystalline, self‑lubricating nature. Nylon, especially when dry, can abrade more and has a higher tendency for stick‑slip.
Filled nylons (MoS₂, PTFE, or oil‑filled) can approach POM’s friction but at added cost.
For bearing design, refer to our Wear and Friction Guide.
4. Moisture Absorption and Dimensional Stability
| Property | Nylon 66 | Nylon 6 | Delrin |
|---|---|---|---|
| Water absorption (24h immersion, 23°C) | 1.2–1.5% | 1.5–1.8% | 0.2–0.3% |
| Saturation (50% RH) | 2.5–3.0% | 3.0–3.5% | 0.2–0.4% |
| Saturation (immersion) | 8–9% | 9–10% | 0.4–0.6% |
| Linear mould shrinkage (typical) | 1.0–1.5% | 0.8–1.4% | 1.8–2.2% (but highly isotropic) |
| Dimensional change from dry to saturated | +0.5–0.7% | +0.6–0.8% | <0.1% |
Practical consequence: Nylon parts in humid environments can swell significantly, altering fit and tolerances. Delrin parts remain stable, making them preferred for precision components in wet or variable‑humidity conditions (e.g., pumps, valves, marine applications).
Pre‑conditioning nylon (moisture equilibration before use) is often required for critical assemblies.
5. Thermal Performance and Continuous Service Temperature
| Property | Nylon 66 | Nylon 6 | Delrin |
|---|---|---|---|
| Heat deflection temperature (HDT, 1.82 MPa, dry) | 90–100°C | 65–80°C | 110–130°C |
| HDT (unannealed, 0.45 MPa) | 200–220°C | 160–180°C | 155–165°C |
| Continuous service temperature (air, 20,000h) | 80–100°C | 75–90°C | 90–105°C |
| Short‑term peak temperature | 180–200°C | 150–170°C | 140–150°C |
| Thermal degradation onset (TGA, air) | ~350°C | ~340°C | ~320°C |
Nylon retains more strength at elevated temperatures (up to 150°C) than Delrin, which begins to soften noticeably above 100°C. For under‑hood automotive components or electrical connectors near heat sources, glass‑filled nylon is often preferred.
For high‑temperature continuous operation (>120°C), consider PEEK or PEI instead. [Internal Link: /materials/peek-pei/]
6. Chemical Resistance
| Chemical class | Nylon 66 | Delrin |
|---|---|---|
| Aliphatic hydrocarbons (oils, greases) | Good | Excellent |
| Aromatic hydrocarbons (toluene, benzene) | Moderate | Good |
| Alcohols | Good | Good |
| Esters, ketones | Poor to moderate | Moderate (some attack) |
| Strong mineral acids | Poor (attacks amide) | Poor (oxidising acids degrade) |
| Strong bases | Poor (hydrolysis) | Good (except very concentrated) |
| Water / steam (long term) | Hydrolyses above 80°C | Stable (but limited to <100°C for long life) |
| UV resistance (unmodified) | Poor (requires stabilisers) | Poor (requires carbon black or UV stabilisers) |
Note: Both materials degrade under UV. For outdoor applications, select UV‑stabilised grades or use black pigmentation.
7. Compatibility with Manufacturing Processes
| Process | Nylon | Delrin |
|---|---|---|
| Injection moulding | Excellent – wide processing window | Excellent – easy flow, low moisture sensitivity |
| CNC machining | Good – but moisture content must be controlled to avoid warping | Excellent – very stable, no moisture issues |
| 3D printing (SLS / MJF) | Yes – many powder grades available | No – not available in powder form for SLS/MJF |
| Extrusion | Good | Good |
For 3D printing of nylon (PA 12, PA 11, glass‑filled), see our 3D Printing Materials page [Internal Link: /services/3d-printing/materials/].
8. Long‑Term Aging and Fatigue
| Property | Nylon 66 (dry) | Delrin |
|---|---|---|
| Fatigue endurance limit (10⁷ cycles, reverse bending, 23°C) | 20–25 MPa | 28–35 MPa |
| Retention after 5000h at 100°C in air | 70–80% (oxidative) | 85–90% |
| Retention after 5000h at 80°C in water | 30–50% (hydrolysis) | >90% |
| Recommended max operating temperature for 10 years | 80–100°C (dry), 60–80°C (wet) | 90°C (continuous) |
Takeaway: Delrin has superior fatigue and long‑term stability in wet or moderate‑temperature environments. Nylon’s fatigue life is highly sensitive to moisture and temperature.
9. Cost Comparison (Indicative, 2026)
| Material | Relative cost per kg (standard unfilled) |
|---|---|
| Nylon 6/6 | 1.0 (baseline) |
| Nylon 6 | 0.9–1.0 |
| Delrin (POM) | 1.1–1.3 |
| Glass‑filled nylon (30%) | 1.2–1.4 |
| Glass‑filled Delrin (30%) | 1.5–1.8 |
| Specialty nylons (PA 46, PPA) | 2.0–3.0 |
Delrin is slightly more expensive than standard nylon but cheaper than high‑temperature nylons. For precision, low‑moisture applications, the added cost may be justified by longer part life and reduced maintenance.
10. Selection Decision Framework
Use the following criteria to choose between nylon and Delrin:
Choose Nylon if:
- Part will be used dry or low humidity (or can be pre‑conditioned)
- 3D printing is required
- Continuous temperature exceeds 100°C (glass‑filled nylon)
- High toughness and impact strength are critical
- Cost is the primary driver (unfilled grades)
- Electrical insulation in dry environments is needed
Choose Delrin if:
- Part operates in wet, high‑humidity, or submerged conditions
- Tight dimensional tolerances must be maintained over time
- Low friction and high wear resistance (unlubricated bearings, gears) are essential
- Machined parts with excellent surface finish are required
- Creep resistance under long‑term static load is important
- Part will be stored or used outdoors with UV‑stabilised grade
Hybrid approach: Use glass‑filled nylon for high‑temperature strength, or oil‑filled / PTFE‑filled Delrin for extreme wear applications.