Nylon vs. POM (Acetal): Engineering Plastics Comparison Guide

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:

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.

耐衝擊性 — 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:

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:

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:

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:

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.

FAQs

Q1: What is the best nylon grade for injection molding?

A: PA66-GF30 is the most widely used grade for structural injection molding parts. PA6 offers good mechanical properties at lower cost. PA12 is best for fluid contact and low-moisture applications.

Q2: How do I prevent moisture problems in nylon parts?

A: Dry nylon to below 0.2% moisture content (80C for 4-6 hours in a desiccant dryer) before processing. Store dried material in sealed containers with desiccant.

Q3: Can nylon be used for food contact applications?

A: Yes, both PA6 and PA66 have FDA food contact approvals (21 CFR 177.1500). EU Regulation 10/2011 compliance is available for KSAN and similar brands.

Q4: What reinforcement provides the best stiffness?

A: Carbon fiber reinforced nylon (CF30) provides 5x the stiffness of unfilled nylon, approaching aluminum. Glass fiber (GF30) provides 3x stiffness at lower cost.

Q5: How does nylon compare to POM for mechanical applications?

A: Nylon has better chemical resistance, higher temperature performance, and superior fatigue resistance. POM has better dimensional stability in humid environments and lower friction.