Material Comparison Guide · Updated August 15, 2026 · Juhai R&D Center

PA6 vs PA66 Nylon — The Complete 2026 Material Comparison Guide (With ISO Test Data)

PA6 and PA66 are the two most common nylons in engineering plastics — but do you really know the practical, measurable differences when selecting a grade for your part? This side-by-side guide compares chemistry, mechanicals, HDT, moisture absorption, cost and 15 real-world case studies so you can select the right polyamide on data, not guesswork.

Table of Contents

1. 1. The Core Chemical Difference (Why It Matters)

2. 2. Full Side-by-Side Property Comparison Table (Unreinforced & 30% GF)

3. 3. Mechanical Performance: Strength, Stiffness and Impact

4. 4. Thermal Performance: HDT, Melting Point and Continuous Use

5. 5. Chemical Resistance & Moisture Absorption

6. 6. Dimensional Stability, Shrinkage & Warpage

7. 7. Injection Molding Processing Parameters Compared

8. 8. Cost-Performance Analysis: PA6 vs PA66 per kg

9. 9. 15 Real-World Application Case Studies

10. 10. 30-Second Decision Checklist

11. 11. 8 Most Frequently Asked Questions (FAQ)

12. 12. Summary & Next Steps

1. The Core Chemical Difference (Why It Matters)

Both PA6 and PA66 are polyamides — long-chain polymers with repeating amide (-CONH-) groups. But the length of the aliphatic carbon chain between those amide groups, and how regularly the hydrogen bonds align, produces all the measurable differences in mechanical and thermal behavior:

PA6 (Nylon 6, Polycaprolactam, CAS 25038-54-4)

• Polymerized by ring-opening of caprolactam monomer (6 carbon atoms).

• Amide groups spaced every 6 carbons along the chain — slightly less dense hydrogen bonding per unit length.

• Lower crystallinity (~30-40%). Lower melting point (Tm ~ 220°C).

• Lower melt viscosity at equal temperature → better flow and surface finish in molding.

PA66 (Nylon 66, Polyhexamethylene Adipamide, CAS 32131-17-2)

• Condensation polymer of hexamethylenediamine (6C diamine) + adipic acid (6C diacid) — hence "6,6".

• More symmetric and tighter chain packing → denser, more regular hydrogen bonding.

• Higher crystallinity (~45-50%). Higher melting point (Tm ~ 260°C).

• Superior crystal structure gives higher tensile, higher stiffness and especially 50–60°C higher HDT at equal glass fiber load.

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All values below are Juhai Plastics production-typical tested values on ISO specimens (dry-as-molded, 23°C, 50% RH). Always request a CoC for exact lot data, or contact our R&D for custom test certificates.

3. Mechanical Performance

In the unreinforced state, PA66 is roughly 10–15% stronger than PA6 in every mechanical category — tensile, flexural and impact. Once you add glass fiber (the form you will actually specify 90% of the time for structural parts), the gap narrows to ~12–17 % depending on the property. But there is a critical pattern:

Key Observation: PA6 + 35% GF ≈ PA66 + 30% GF on most mechanicals

This is the single most under-appreciated fact in nylon grade selection. If your drawing currently says "PA66 GF30, tensile ≥ 180 MPa", you can usually match that by going to PA6 GF35 at a 20–25% lower per-kilogram cost. At Juhai, this is exactly how our PA6 GBA35 (35% GF Cost-Optimized) grade often displaces premium PA66 GF30 at medium-load structural bracket customers.

4. Thermal Performance

Thermal performance is where PA66 earns its premium. The difference in HDT (heat deflection temperature) is ~50°C at 1.82 MPa even at equal GF loading. Translated to product reliability:

• PA6 GF30 is safe for continuous 100–120°C, short peak up to 190°C. Covers the vast majority of appliance, power tool, general electronic and industrial bracket heat requirements.

• PA66 GF30 is required for continuous 140–170°C, short peak up to 250°C. Automotive under-hood (intake manifolds, engine covers), high-power relay bobbins, near-motor components, industrial cookware structural parts.

Quick Thermal Litmus Test

If you cannot hold your gloved hand on the hottest exposed location of the working part for 3 seconds (> 60°C surface), but boiling water poured on it does NOT deform it (≤ 100°C continuous) → PA6 is sufficient. If boiling water or a 150°C oven heat test shows deflection → PA66 or PA6/66 blend.

5. Chemical Resistance & Moisture Absorption

Both PA6 and PA66 have excellent resistance to:

• Hydrocarbons (gasoline, diesel, motor oil, gear oil, hydraulic fluid)

• Most alcohols, weak acids and weak alkalis at room temperature

• Chlorinated solvents, refrigerant gases, ester-based lubricants

Both degrade in:

• Strong mineral acids (H₂SO₄, HCl) and strong alkalis (NaOH 50% at elevated T)

• Phenolic compounds and calcium chloride solutions at > 60°C (stress cracking)

• Bleaching solutions containing active chlorine

The main practical difference is moisture absorption: PA6 absorbs marginally more moisture than PA66 (see table above). After 500 hours at 85°C/85% RH, PA6 GF30 tensile drops ~8 % vs PA66 GF30 which drops ~5 %. If your application is a high-humidity tropical outdoor environment with close tolerance snap fits, a small PA66 advantage justifies evaluation. For typical < 60 % RH indoor use the effect is negligible.

6. Dimensional Stability & Shrinkage

Unreinforced PA66 actually shrinks MORE than unreinforced PA6 — a persistent myth that the "higher performance" PA66 should shrink less. This reverses once you add glass fiber: GF-filled PA66 has slightly LESS flow-direction shrinkage (0.30 vs 0.35 %). But both materials' real dimensional issue is ANISOTROPIC shrinkage — cross-direction shrinkage is 2.5-3× the flow-direction shrinkage. This is the #1 cause of warpage in GF-nylon parts. Our defects troubleshooting guide covers this in depth with mold temperature and gate fixes.

7. Injection Molding Processing Parameters Compared

Processing cost: PA66 will cost you ~3-5 % more per shot in higher electricity consumption (higher barrel temps) and longer cycle time. For a 500-Ton press running 24/7, this is a non-trivial 4- to 5-figure annual cost on top of the raw-material premium.

8. Cost-Performance Analysis

Scenario: a medium-volume automotive bracket project, 50,000 parts / year, 85 grams each, 30% GF required:

On this typical 4-ton-per-year bracket project, PA6 is over USD 2,300 per year cheaper, and Juhai's 35% GF cost-optimized PA6 grade saves over $ 4,100 per year with mechanicals that exceed PA66 GF30's tensile (138 MPa for our PA6 GBA35 vs 190 MPa for premium PA66 GF30 — we do transparently publish the spec, so please check if PA6 GF35 meets your actual load; we will tell you honestly if it doesn't.)

9. 15 Real-World Application Case Studies

Applications where PA6 is the BETTER choice (9 of 15):

1. Consumer-grade power tool gearbox housing (class B surface, 110°C HDT sufficient)

2. Office furniture height-adjustment mechanism bracket

3. Reel and spool components for fishing tackle (impact > 12 kJ/m² is enough)

4. Domestic washing machine detergent dispenser drawer housing

5. Electric bicycle battery lower case structural frame (room temp)

6. Industrial conveyor belt idler pulley (PA6 GF35 matches competitor PA66 GF30 in testing)

7. Light-duty cable cleat and ladder tray fastener

8. Kitchen blender drive shaft coupler (low heat, snap-fit critical)

9. Automotive secondary interior dashboard mounting bracket (hidden, 80°C max)

Applications where PA66 is the CORRECT choice (6 of 15):

10. Automotive intake manifold — direct contact 140°C coolant lines and vibration creep

11. Terminal block and relay base with 125°C continuous operating temp per IEC standard

12. Heavy-duty industrial ratchet wrench gear cage (max fatigue strength)

13. Industrial cooker deep-fryer structural bracket (150°C continuous use)

14. 2.5 kV high-voltage bushing and insulator requiring UL 746B 130°C RTI

15. Automotive door check strap / hinge bearing washer (high creep load + winter -40°C)

10. 30-Second Decision Checklist: PA6 or PA66?

11. 8 Most Frequently Asked Questions

Jump directly to the full plastic material FAQ section on the blog home page, or read the expanded 8 PA6-vs-PA66 specific FAQs (with structured data for Google People Also Ask).

12. Summary & Next Steps

In one sentence: If your application can live within PA6's HDT and you're optimizing total cost, PA6 (especially 35% GF cost-optimized) is almost always the rational engineering choice. If you need every last degree of heat resistance and creep stiffness — or an existing standard locks you in — PA66 GF is worth every penny of its premium. Not sure where your part falls? Juhai's R&D engineers will read your drawing, review your spec, and recommend a grade with actual expected performance numbers and sample test results — all free of charge, within 24 hours of you contacting us.