PA6 vs PA66: Complete Comparison Guide for Engineers and Buyers

**PA6 (Nylon 6)** is produced by ring-opening polymerization of caprolactam, with 6 carbon atoms in the molecular chain. Melting point ~220°C, density 1.13 g/cm³, moisture absorption ~3.5% (23°C/24h equilibrium).

**PA66 (Nylon 66)** is produced by condensation polymerization of hexamethylenediamine and adipic acid, with two groups of 6-carbon chains per repeating unit. Melting point ~260°C, density 1.14 g/cm³, moisture absorption ~2.5%.

**Key Differences:** - Melting Point: PA66 is ~40°C higher than PA6 → better high-temperature resistance - Molecular Symmetry: PA66 has more regular molecular chains → higher crystallinity - Moisture Absorption: PA6 absorbs more water → slightly lower dimensional stability but better toughness - Processing Temperature: PA6 ~240-280°C, PA66 ~260-300°C

**Unreinforced Base Property Comparison:** | Property | PA6 | PA66 | |----------|-----|------| | Tensile Strength | 75 MPa | 82 MPa | | Flexural Modulus | 2.5 GPa | 3.0 GPa | | Notched Impact Strength | 6 kJ/m² | 5 kJ/m² | | HDT (1.8MPa) | 65°C | 75°C | | Molding Shrinkage | 0.7-1.5% | 1.0-2.0% |

**When to Choose PA6:** - High impact toughness required (automotive bumpers, power tool housings) - Good wear resistance needed (gears, bearings, pulleys) - Low-temperature applications (PA6 has lower brittle temperature) - Better dimensional accuracy needed (lower molding shrinkage)

**When to Choose PA66:** - High rigidity and strength required (structural parts, under-hood components) - Long-term high-temperature use (engine intake manifolds, radiator tanks) - Better chemical resistance needed (fuel system parts, brake fluid contact) - Higher heat deflection temperature required

**Performance After Glass Fiber Reinforcement:** - PA6-GF30: Tensile strength up to 180 MPa, flexural modulus 10 GPa - PA66-GF30: Tensile strength up to 200 MPa, flexural modulus 12 GPa - PA66-GF50: Tensile strength up to 250 MPa, flexural modulus 17 GPa

**Rule of Thumb:** If the part operates above 120°C long-term, choose PA66; if it needs to withstand impact loads or operate below -20°C, choose PA6.

**Continuous Use Temperature (CUT):** - PA6 unreinforced: 80-100°C - PA6-GF30: 120-140°C - PA66 unreinforced: 100-120°C - PA66-GF30: 140-160°C - PA66-GF50: 150-170°C

**Heat Deflection Temperature (HDT @ 1.8MPa):** - PA6: 65°C → 210°C after GF30 reinforcement - PA66: 75°C → 240°C after GF30 reinforcement

**UL Temperature Index (RTI):** - PA6-GF30: 130°C (electrical) / 110°C (mechanical impact) - PA66-GF30: 140°C (electrical) / 120°C (mechanical impact)

**Real Application Cases:** - Automotive under-hood: PA66-GF35 (intake manifold, throttle body) → 150°C long-term - EV connectors: PA66-GF25 FR → 125°C long-term + flame retardant - Power tool housing: PA6-GF30 → intermittent 120°C + high impact - Water heater parts: PA6-GF50 → 80°C long-term + hydrolysis resistant

**Moisture Absorption Comparison (23°C/24h equilibrium):** - PA6: 3.5% - PA66: 2.5% - PA6-GF30: 1.8% - PA66-GF30: 1.4%

**Effects of Moisture on Properties:** - Dimensional swelling: PA6 swells ~2% by volume, PA66 ~1.5% - Strength reduction: PA6 tensile strength drops 15-20% wet, PA66 drops 10-15% - Toughness increase: PA6 impact strength actually increases 30-50% when wet (pros and cons)

**Applications Requiring High Dimensional Accuracy:** - Precision gears → PA66-GF (low absorption + high rigidity) - Electronic connectors → PA66-GF FR (low absorption + flame retardant + high CTI) - Optical components → Consider PBT or PPS alternatives

**Applications Requiring High Toughness:** - Sports equipment → PA6-GF (better toughness when wet) - Ski boot buckles → PA6 (utilizes moisture-induced toughening) - Textile machinery parts → PA6 (self-lubricating + wear resistant)

**Moisture Conditioning:** PA6 and PA66 parts should undergo moisture conditioning (80°C hot water soak for 2-4 hours) after molding to reach equilibrium moisture content and prevent dimensional changes during use.

**Raw Material Price Comparison (2026 China Market):** - PA6 pure resin: ¥18-22/kg - PA66 pure resin: ¥22-28/kg - PA6-GF30: ¥22-26/kg - PA66-GF30: ¥26-32/kg - PA66-GF50: ¥30-38/kg

**Reasons for Price Difference:** - PA66 raw material adipic acid depends on imports, high price volatility - PA6 raw material caprolactam has high domestic production rate, stable supply - PA66 processing temperature is higher, energy cost increases 5-8%

**Total Cost of Ownership (TCO) Considerations:** - If PA6 meets performance requirements, choosing PA6 saves 10-20% material cost - If PA66 lifespan is 2x PA6 (high-temp environment), PA66 is more economical - After GF reinforcement, price gap narrows to 5-10%

**Cost Reduction Suggestions:** 1. Precisely evaluate temperature and mechanical requirements to avoid over-engineering 2. Consider PA6-GF as alternative to PA66-GF (similar performance, 10-15% lower cost) 3. Bulk purchasing (20+ tons) can get 5-8% discount 4. Choose compounding factory direct supply (skip trader markup)

**Jinsu** provides full range of PA6/PA66 modified materials (GF15/GF30/GF50/flame retardant/toughened), monthly capacity 3000+ tons, ISO 9001 certified, directly addressing end customer technical requirements.