PA6 vs PA66: Complete Comparison Guide for Engineers

**PA6 (Nylon 6)** is produced by ring-opening polymerization of caprolactam, with 6 carbon atoms in the molecular chain. Melting point ~220°C (428°F), 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 (500°F), density 1.14 g/cm³, moisture absorption ~2.5%.

**Key Differences:** - Melting Point: PA66 is ~40°C (72°F) 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 (464-536°F), PA66 ~260-300°C (500-572°F)

**Unreinforced Base Property Comparison:**

**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.

**From Our Experience:** In our experience supplying automotive Tier-1 clients, switching from PA66-GF30 to PA6-GF30 for non-critical brackets saved 15% cost without field failures - provided the operating temperature stays below 120°C.

Need high-impact PA6-GF for power tools? Request Impact Test Report + Sample

**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

Sourcing heat-resistant PA66-GF for EV connectors? Download UL Yellow Card & TDS

**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 (per ISO 1110):** PA6 and PA66 parts should undergo moisture conditioning to reach equilibrium moisture content (80°C hot water soak for 2-4 hours, ISO 1110 accelerated conditioning), preventing dimensional changes during use.

**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)

Looking to reduce nylon material cost by 10-15%? Get Custom Cost-Saving Proposal

**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.

Not sure which nylon fits your application? Walk through this decision tree:

1. Operating temperature above 120°C continuous? → YES → PA66-GF30/GF50 → go to step 4 2. Below 120°C but high impact or -20°C low-temperature service? → YES → PA6-GF30 (toughened if needed) 3. Neither extreme? Compare cost and dimensional requirements → PA6-GF30 if cost-driven; PA66-GF30 if stiffness and creep resistance matter 4. Electrical application? → FR grade: PA66-FR (V-0, high CTI) or PA6-FR 5. Hot coolant or hydrolysis exposure? → hydrolysis-resistant PA66

**Quick Rules:** - Gears/bearings: PA66-GF (low absorption, dimensional stability) or PA6 wear-resistant grade - Power tools: PA6-GF30 (impact + cost balance) - Under-hood: PA66-GF30+ (heat) - Non-critical brackets: PA6-GF30 (save 10-15%)

**Recycled PA6 vs PA66:** Both polymers can be compounded with post-industrial or post-consumer recycled content. Recycled PA6 is more common because caprolactam depolymerization is mature; recycled PA66 quality depends on the source stream. Jinsu offers recycled-content PA6-GF30 and PA66-GF30 (20-50% PCR) that meet virgin-grade mechanical targets.

**Bio-based nylon:** PA6 from bio-based caprolactam (castor-oil route) and partially bio-based PA66 are available. Bio-PA6 reduces scope-3 carbon by ~30-40%.

**Carbon footprint & CBAM:** With EU CBAM expanding, buyers now ask for carbon footprint data per ton of polymer. Recycled-content grades typically cut CO₂ by 30-60% vs virgin. Ask your supplier for a carbon footprint statement with the COA.

**Jinsu's sustainability offer:** PCR-content FR-PA and GF-PA grades, carbon footprint documentation, and mass balance documentation support on request. Talk to our sustainability desk

Buyers often spec BASF Ultramid or Envalior (formerly DSM) Akulon grades. The table below benchmarks Jinsu grades against the most common international equivalents:

**Drop-in compatibility:** Jinsu grades are engineered as direct drop-in replacements. Processing parameters (drying, melt temperature, mold temperature) are compatible with equivalent international grades, and our technical team is available for molding trial support - no more "same datasheet, hard to mold" surprises.

Currently using Ultramid B3WG6 or Akulon K225-FR? Request Free Equivalent Sample + Full Validation Report - verify drop-in replacement in your existing mold.

**Why buyers switch:** Jinsu halogen-free FR grades match or exceed the CTI (≥600V) of the Envalior equivalents with higher tensile strength, at lower cost.

Most nylon part failures trace back to four root causes:

**1. Insufficient drying before molding.** PA6/PA66 absorb moisture fast; molding wet pellets causes splay marks, brittleness, and hydrolysis-driven strength loss. Dry to <0.1% moisture (80-90°C, 4-6h) before molding.

**2. Hydrolysis in hot, humid service.** PA66 in hot coolant or steam loses strength via chain scission. Use hydrolysis-resistant PA66 or PA66-GF with hydrolysis stabilizers.

**3. Stress cracking under snap-fits.** Glass-filled nylons have low elongation; aggressive snap-fit designs crack. Add draft, radius, and use impact-modified grades for assembly-critical parts.

**4. Warpage from unbalanced shrinkage.** PA66-GF warps more than PA6-GF in asymmetric parts. Redesign gates/ribs or switch to PA6-GF for flat thin-wall parts.

If a nylon part failed in your application, send us the part and failure photos - our lab will run root-cause analysis (FTIR, DSC, SEM) and recommend the stabilized formulation.

Four things processors care about when switching nylons:

- **Drying:** PA6 requires stricter drying (<0.1% moisture) vs PA66 - both must be dried, but PA6 picks up moisture faster after drying, so dry right before molding - **Mold shrinkage:** PA6 lower shrinkage (0.7-1.5%) → better dimensional control in thin-wall parts; PA66 (1.0-2.0%) needs more shrinkage allowance - **Cycle time:** PA6 crystallizes faster → shorter cycle time, higher throughput - **Tool wear:** PA66-GF is more abrasive → hardened steel molds recommended for long production runs

**Typical processing parameters:** melt temperature PA6 240-280°C (464-536°F), PA66 260-300°C (500-572°F); mold temperature 60-90°C; medium injection speed. Jinsu provides molding trial support and process optimization on request.