Head-to-head comparison of nylon and POM (acetal/delrin) for engineering applications — mechanical, thermal, chemical, wear, and processing differences.
Nylon vs. POM: Two Giants of Engineering Plastics
Nylon (polyamide) and POM (polyoxymethylene, also called acetal or Delrin) are the two most-used engineering thermoplastics for mechanical components. Both offer excellent wear resistance, low friction, and good dimensional stability — but their different molecular structures create distinct performance trade-offs that matter enormously in precision applications.
Choosing between nylon and POM is not trivial. A bearing that lasts 50,000 cycles in POM may fail in 8,000 cycles in nylon under the same load. Conversely, a gear housing exposed to automotive fluids will crack with POM but survive with PA66. This guide provides the data-driven comparison engineers need to make the right choice.
Mechanical Properties Comparison
**Tensile and Flexural Properties**:
| Property | PA6 | PA66 | POM (Homopolymer) | POM (Copolymer) |
|—|—|—|—|—|
| Tensile Strength (MPa) | 80 | 82 | 70 | 62 |
| Tensile Modulus (GPa) | 2.8 | 3.0 | 2.8 | 2.5 |
| Flexural Strength (MPa) | 100 | 110 | 98 | 90 |
| Flexural Modulus (GPa) | 2.6 | 2.8 | 2.6 | 2.3 |
| Elongation at Break (%) | 150 | 60 | 40 | 35 |
| Notched Izod (J/m) | 55 | 45 | 75 | 65 |
| Creep Modulus (1000h, 20 MPa) | 1.2 GPa | 1.4 GPa | 2.3 GPa | 2.0 GPa |
**Key Insight: Creep Resistance** — POM has significantly better creep resistance than nylon. Under sustained loading, POM retains more of its stiffness over time. For components under constant load (spring clips, retaining rings, fastener bushings), POM’s superior creep resistance often makes it the better choice despite similar initial strength.
**Impact Resistance** — Nylon has higher unnotched impact resistance. But POM often outperforms nylon in notched impact tests because POM’s ductile failure mode absorbs more energy at the crack tip. For parts with stress concentrations (keyways, holes, threads), POM’s toughness at sharp notches is an advantage.
**Fatigue Resistance** — Nylon has superior fatigue resistance for repeated loading. In cyclic loading tests, nylon components survive 3-5× more cycles before failure than equivalent POM parts. Critical for components like conveyor belt guides, pump impellers, and hinge mechanisms.
Thermal and Environmental Performance
**Thermal Properties**:
| Property | PA6 | PA66 | POM |
|—|—|—|—|
| Melting Point (°C) | 225 | 265 | 175 |
| Continuous Service Temp (°C) | 100-115 | 130-150 | 90-100 |
| HDT @ 1.82 MPa (°C) | 65 | 90 | 95 |
| HDT @ 0.45 MPa (°C) | 170 | 250 | 160 |
| Thermal Expansion (×10⁻⁵/°C) | 8-9 | 8-9 | 11-12 |
**POM’s thermal weakness** — The 175°C melting point of POM is its thermal limitation. At temperatures above 100°C, POM loses mechanical strength rapidly. PA66-GF30 (HDT 250°C) operates at temperatures where POM would melt.
**Moisture Absorption Comparison**:
| Property | PA6 | PA66 | POM |
|—|—|—|—|
| Saturation Moisture (%) | 9.5% | 8.5% | 0.8% |
| Dimensional Change (saturation) | 1.5-2.0% | 1.3-1.8% | 0.2% |
**POM wins decisively on moisture** — At 0.8% maximum moisture absorption, POM is essentially dimensionally stable in humid environments. Nylon’s 8-9% absorption causes measurable swelling and property changes. For underwater or outdoor exposed applications without encapsulation, POM is often the only viable choice.
Chemical Resistance: Where Each Material Excels
**Chemical Resistance Comparison**:
| Chemical | Nylon (PA66) | POM |
|—|—|—|
| Gasoline/Fuels | Excellent | Excellent |
| Motor Oil | Excellent | Excellent |
| Brake Fluid | Good | Poor (swells) |
| Alcohol | Excellent | Good |
| Ketones (Acetone) | Good | Poor (dissolves) |
| Weak Acids | Fair | Good |
| Strong Acids | Poor | Poor |
| Esters/Plasticizers | Excellent | Poor |
| Hot Water (>60°C) | Poor | Good |
| Steam | Poor | Poor |
**Critical Decision Points**:
– **Brake fluid or glycol coolants**: POM swells and cracks — use PA66 or PA12
– **Hot water (>60°C)**: Nylon hydrolyzes — use POM or PVDF
– **Plasticizer migration** (flexible cables, wire insulation): POM absorbs plasticizers — use PA12
– **Automotive under-hood**: PA66-GF30 for its heat resistance (180°C+) and fluid resistance
– **Consumer appliances**: POM for its dimensional stability and surface finish
Wear and Friction Performance
Both materials offer low friction and good wear resistance — but with important differences:
| Property | PA6 | PA66 | POM |
|—|—|—|—|
| Coefficient of Friction (vs. steel, dry) | 0.25-0.40 | 0.20-0.35 | 0.15-0.35 |
| PV Limit (MPa·m/min) | 80-120 | 90-130 | 80-100 |
| Wear Factor (vs. steel, dry) | 15-40 | 10-30 | 1-3 |
| Machinability | Good | Excellent | Excellent |
**The critical difference: wear factor** — POM’s wear factor (1-3) is 10-20× lower than nylon’s (10-40). This means POM parts generate less heat and wear more slowly in sliding contact. For high-PV applications (bearings, wear strips, sliding inserts), POM is the superior choice.
**Self-lubricating versions**:
– **POM + PTFE**: Wear factor drops to 0.5-1.0 — excellent for boundary lubrication
– **PA6/66 + PTFE or silicone**: Significantly reduces friction, but PTFE can migrate to surface and affect bonding
– **Carbon fiber reinforced**: Improves wear resistance in both materials, especially at elevated temperatures
**Surface Speed Consideration**: At surface speeds above 1 m/s in dry sliding, both materials generate enough heat to cause thermal softening. For high-speed applications, consider internally lubricated grades or oil-impregnated sintered bronze backings.
How to Choose: Decision Framework
**Choose Nylon (PA66-GF30) when:**
– Operating temperature exceeds 100°C
– Repeated impact or cyclic loading is expected
– Exposure to brake fluid, coolants, or plasticizers
– You need higher fatigue life in dynamic loading
– Cost is the primary driver (PA66 is generally less expensive than POM)
**Choose POM when:**
– Dimensional stability in humid environments is critical
– Low friction and low wear factor are priorities (sliding/rotating contact)
– Parts will be exposed to hot water or steam
– Acetone, esters, or plasticizers are present
– You need excellent surface finish and tight tolerances
**Hybrid Solution — Metal Replacement**:
For many metal-replacement applications, the choice is not between nylon and POM, but between them and aluminum. Nylon-GF and POM are both excellent metal substitutes for housings, brackets, and structural components, offering 70-85% weight reduction vs. aluminum with adequate strength. For these applications, PA66-GF30 is the default choice due to its superior thermal and fluid resistance.
Whether you need technical guidance on selecting the right nylon grade for your specific application, or want to discuss pricing and supply options for PA6-CF, PA66-GF, or standard nylon materials, our engineering team is ready to help. Nylonplastic.com supplies industrial-grade nylon materials to manufacturers in North America, Europe, and Southeast Asia.
Get a Free Material Consultation →
Contact our technical team for nylon grade recommendations, pricing for bulk orders, or samples for testing. We supply PA6-CF carbon fiber reinforced nylon in 1.75mm and 2.85mm diameters, plus full range of PA6, PA66, PA12, and GF-reinforced grades.
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**FAQs**
**Q: What is the difference between PA6 and PA66?**
A: PA66 (nylon 66) has a higher melting point (265°C vs. 225°C) and better chemical resistance than PA6. PA6 offers better impact resistance and is more cost-effective. PA66 is preferred for high-temperature and under-hood automotive applications; PA6 is common for general engineering.
**Q: How much does glass fiber reinforcement improve nylon?**
A: Adding 30% glass fiber increases tensile strength by 100-120% (from ~80 MPa to ~170 MPa) and flexural modulus by 250-300% (from ~2.8 GPa to ~9 GPa). However, it also reduces impact resistance and increases warpage.
**Q: What is carbon fiber reinforced nylon used for?**
A: Carbon fiber reinforced nylon is used for structural components requiring high stiffness-to-weight ratio, ESD-sensitive applications (electronics packaging, fuel systems), and precision parts requiring dimensional stability. nylonplastic.com supplies PA6-CF for FDM 3D printing and injection molding applications.
**Q: How do I prevent moisture absorption problems in nylon parts?**
A: Dry nylon resin to below 0.2% moisture content before molding (4-6 hours at 80-85°C in desiccant dryer). For dimensional-critical parts, anneal after molding (1-2 hours at 120-130°C) to stabilize crystallinity. Use glass or carbon fiber reinforcement to reduce moisture-induced dimensional change by 70-80%.
**Q: Can nylon be used for food contact applications?**
A: Yes. Both PA6 and PA66 have FDA 21 CFR §177.1500 compliance for food contact. EU Regulation 10/2011 compliance requires specific compound selection with documented SML testing. Always verify specific grade compliance with your supplier.
