Delrin (Acetal) vs Nylon: 6-Point Selection Guide

Which Material Should You Choose?Choose Delrin (Acetal if:Precision gears, bearings, bushings, fasteners, snap-fits, conveyor componentsapplications requiring dimensional stability, low friction, stiffness, and fatigue resistance in dry or humid...

Delrin (acetal homopolymer, POM) and Nylon (polyamide 66, PA66) are the two most-specified engineering thermoplastics for precision mechanical components — gears, bearings, bushings, fasteners, and structural parts. Both are strong, tough, and easy to machine, which leads to frequent confusion about which to specify. The choice comes down to three questions: Will the part be exposed to moisture? (Choose Delrin.) Does the part need maximum impact toughness or higher temperature? (Choose Nylon.) Is dimensional stability critical? (Choose Delrin.) This 6-point selection guide breaks down the trade-offs with the property data that matters for real mechanical design.

1. Dimensional Stability & Water Absorption — Delrin's Decisive Advantage

Moisture absorption is the single biggest difference between Delrin and Nylon in service. Nylon absorbs 2.5-3.5% water at equilibrium (50% RH, 23°C), causing dimensional swelling of 0.5-2.0% and a 30-50% drop in modulus and strength. This means a precision nylon gear machined to ±0.05mm tolerance in a dry shop may swell out of tolerance in a humid environment. Delrin absorbs only 0.2% water — 10-15x less than nylon — and its dimensions are essentially unaffected by humidity. For any precision mechanism operating in a humid environment, or any part that must hold tight tolerances regardless of moisture (gears, bearings, gauges, instrument housings), Delrin is the correct choice. Nylon's moisture sensitivity can be mitigated by conditioning (boiling in water to pre-saturate) or by using glass-filled grades, but Delrin eliminates the problem entirely.

2. Property Comparison Table

Data reflects unfilled Delrin 500P and unfilled PA66. Glass-filled and PTFE-filled grades significantly change properties. See our pom-delrin-acetal-properties/">Delrin acetal properties guide and nylon material guide for grade-specific data.

3. Wear Resistance & Friction

Both Delrin and Nylon are excellent bearing and wear materials, but Delrin has the edge in precision sliding applications. Delrin's friction coefficient (0.15-0.20 vs steel) is lower than nylon's (0.20-0.30), and Delrin maintains its friction properties consistently regardless of humidity — nylon's friction increases when wet. Delrin also has better fatigue resistance, making it the standard for snap-fit mechanisms, living hinges, and conveyor chain links that flex repeatedly. Nylon's advantage is its toughness: it absorbs impact better than Delrin, making it preferred for gears that experience shock loads (power tools, automotive starters). For low-friction precision sliding (bushings, gears, sliding mechanisms), Delrin is the default; for high-impact or high-load gears, nylon (especially cast nylon) is preferred.

4. Fatigue Resistance — Delrin's Specialty

Delrin has exceptional fatigue resistance — it can withstand millions of flex cycles without cracking, which is why it is the standard material for snap-fit fasteners, living hinges, clip mechanisms, and chain links. Nylon also has good fatigue resistance, but its moisture absorption causes property changes that complicate long-term fatigue performance in humid environments. For any application involving repeated flexing (snap-fits, springs, clips, chain links, conveyor components), Delrin is the preferred material. This is a decisive advantage in consumer product design and industrial machinery where snap-fit assembly is used.

5. Machining & Processing

Both materials machine beautifully with sharp carbide tooling, producing clean, precise parts. Delrin is the easier of the two to machine: it produces crisp chips, holds tight tolerances, and does not absorb coolant (which simplifies machining coolant selection). Nylon can be machined to similar precision, but its moisture absorption means parts must be measured in controlled humidity, and coolant selection matters (water-based coolants will swell nylon during machining). Both materials injection-mold well. Critical processing warning for Delrin: it degrades exothermically above 230°C, releasing formaldehyde gas — never shut down a barrel containing Delrin; purge with HDPE first. Nylon requires drying (80°C, 4 hours) before processing to prevent hydrolysis and silver streaking.

6. Price & Cost-Effectiveness

Nylon is roughly 20-30% cheaper than Delrin ($3-8/kg vs $5-10/kg). For high-volume applications where Delrin's specific advantages (dimensional stability, fatigue resistance, low friction) are not required, nylon's lower cost is a meaningful advantage. For precision mechanisms, snap-fits, or humid-environment applications where Delrin's properties are essential, the cost premium is easily justified by eliminating the dimensional and performance problems that nylon's moisture absorption causes. The cost decision should always follow the performance decision: first determine whether moisture stability or fatigue resistance is required, then choose accordingly.

Application Scenarios

When to Choose Delrin vs Nylon

Choose Delrin when: (1) the part operates in a humid or wet environment and must hold tight tolerances — gears, bearings, instrument parts; (2) the part involves repeated flexing (snap-fits, living hinges, clips, chain links) where fatigue resistance is critical; (3) low friction and consistent friction properties are needed regardless of humidity; (4) the part is a precision mechanism where dimensional stability over time matters; (5) ease of machining and coolant compatibility matter.

Choose Nylon when: (1) the part experiences impact or shock loads (power tool gears, automotive components); (2) higher temperature resistance is needed (nylon's Tm is 265°C vs Delrin's 175°C); (3) cost is a primary constraint and moisture absorption is acceptable or can be managed; (4) the part is structural and benefits from nylon's higher toughness; (5) the part will be glass-fiber reinforced (GF nylon has exceptional strength-to-weight ratio). For most general mechanical applications, either material works — the choice comes down to moisture, fatigue, and cost.

Compare More Materials

For related mechanical plastic comparisons, see our nylon-vs-acetal-comparison/">Nylon vs Acetal comparison, pom-delrin-vs-pa6-nylon-gears/">POM Delrin vs PA6 Nylon for gears, and delrin-homopolymer-vs-acetal-copolymer-comparison/">Delrin homopolymer vs acetal copolymer comparison for grade-specific Delrin selection. For a deeper look at each material, see our pom-delrin-homopolymer/">Delrin homopolymer guide and pa66-nylon-66-unfilled/">PA66 nylon 66 guide.

Comparison at a Glance

Equivalents & Cross-References

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org