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. The Core Chemical Difference (Why It Matters)
- 2. Full Side-by-Side Property Comparison Table (Unreinforced & 30% GF)
- 3. Mechanical Performance: Strength, Stiffness and Impact
- 4. Thermal Performance: HDT, Melting Point and Continuous Use
- 5. Chemical Resistance & Moisture Absorption
- 6. Dimensional Stability, Shrinkage & Warpage
- 7. Injection Molding Processing Parameters Compared
- 8. Cost-Performance Analysis: PA6 vs PA66 per kg
- 9. 15 Real-World Application Case Studies
- 10. 30-Second Decision Checklist
- 11. 8 Most Frequently Asked Questions (FAQ)
- 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.
2. Full Side-by-Side Property Comparison Table
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.
| Property | Test Standard | PA6 Unreinforced | PA66 Unreinforced | PA6 + 30% GF | PA66 + 30% GF |
|---|---|---|---|---|---|
| Tensile Strength (MPa) | ISO 527 | 78 | 85 (+9%) | 162 | 190 (+17%) |
| Tensile Modulus (MPa) | ISO 527 | 2,700 | 3,100 (+15%) | 8,500 | 9,600 (+13%) |
| Elongation at Break (%) | ISO 527 | 120 | 60 (-50%) | 2.5 | 2.3 (-8%) |
| Notched Izod Impact kJ/m² 23°C | ISO 180/1A | 4.5 | 5.5 (+22%) | 12 | 14 (+17%) |
| Flexural Strength (MPa) | ISO 178 | 110 | 120 (+9%) | 245 | 275 (+12%) |
| Flexural Modulus (MPa) | ISO 178 | 2,500 | 2,900 (+16%) | 7,600 | 8,800 (+16%) |
| HDT @ 1.82 MPa (°C) | ISO 75/Af | 65 | 90 (+38%) | 190 | 250 (+32%) |
| Vicat B/50 (°C) | ISO 306 | 175 | 205 (+17%) | 208 | 243 (+17%) |
| Melting Point Peak °C | DSC | 220–222 | 260–265 | 222 | 263 |
| Shrinkage Flow / Cross % | ISO 294-4 | 1.2 / 1.4 | 1.4 / 1.6 | 0.35 / 0.95 | 0.30 / 0.90 |
| Density g/cm³ | ISO 1183 | 1.13 | 1.14 | 1.35 | 1.37 |
| Water Absorption 24 h % | ISO 62 | 1.9 | 1.6 (-16%) | 1.0 | 0.9 |
| Surface Hardness Rockwell R | ISO 2039-2 | R 118 | R 120 | R 119 | R 121 |
| Approx. Premium Price USD/kg | 2026 Mid-Year | $ 2.25 | $ 2.80 (+24%) | $ 2.10 | $ 2.65 (+26%) |
| Cost-Optimized-GF Price USD/kg (Juhai) | 2026 Mid-Year | $ 1.60 | $ 2.00 | $ 1.50 (BFE06) | $ 1.95 |
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
| Barrel Temp | PA6 = 240–265°C, PA66 = 270–295°C | PA66 is ~30°C hotter across the barrel profile |
|---|---|---|
| Mold Temp | PA6 = 60–90°C, PA66 = 80–110°C | PA66 mold hotter for good surface and crystallization |
| Drying | Both identical: 80°C × 4h to ≤ 0.08 % moisture (dehumidifying dryer mandatory) | |
| Cycle Time | ~10–15% longer for PA66 because hotter melt takes longer to cool to ejection temperature | |
| Melt Decomposition | Keep barrel residence time ≤ 6 min for both; 5 min at top of range for PA66 to avoid discoloration | |
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:
| Annual resin (kg) | 50,000 × 0.085 = 4,250 kg |
|---|---|
| Option A — Premium PA66 GF30 | 4,250 × $ 2.65 = $ 11,263 / year |
| Option B — Premium PA6 GF30 | 4,250 × $ 2.10 = $ 8,925 / year (saves $ 2,338) |
| Option C — Juhai Cost-Optimized PA6 GF35 | 4,250 × $ 1.68 = $ 7,140 / year (saves $ 4,123 vs PA66) |
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):
- Consumer-grade power tool gearbox housing (class B surface, 110°C HDT sufficient)
- Office furniture height-adjustment mechanism bracket
- Reel and spool components for fishing tackle (impact > 12 kJ/m² is enough)
- Domestic washing machine detergent dispenser drawer housing
- Electric bicycle battery lower case structural frame (room temp)
- Industrial conveyor belt idler pulley (PA6 GF35 matches competitor PA66 GF30 in testing)
- Light-duty cable cleat and ladder tray fastener
- Kitchen blender drive shaft coupler (low heat, snap-fit critical)
- Automotive secondary interior dashboard mounting bracket (hidden, 80°C max)
Applications where PA66 is the CORRECT choice (6 of 15):
- Automotive intake manifold — direct contact 140°C coolant lines and vibration creep
- Terminal block and relay base with 125°C continuous operating temp per IEC standard
- Heavy-duty industrial ratchet wrench gear cage (max fatigue strength)
- Industrial cooker deep-fryer structural bracket (150°C continuous use)
- 2.5 kV high-voltage bushing and insulator requiring UL 746B 130°C RTI
- Automotive door check strap / hinge bearing washer (high creep load + winter -40°C)
10. 30-Second Decision Checklist: PA6 or PA66?
| ⓵ Continuous use temp > 140°C? | YES → PA66 · NO → go to ⓶ |
|---|---|
| ⓶ Sustained structural load > 80 MPa? | YES → PA66 · NO → go to ⓷ |
| ⓷ Customer spec explicitly requires PA66? | YES → PA66 · NO → go to ⓸ |
| ⓸ Can you accept 5 % lower tensile for 25 % lower cost? | YES → PA6 (or PA6 GF35 ≈ PA66 GF30 for same price) |
| ⓹ Still unsure? | → Send part drawing + load case to Juhai R&D for free simulation-based grade recommendation within 24h. |
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).
No, PA66 is NOT universally better than PA6. PA66 wins on mechanical and heat performance (tensile +10-15%, HDT ~50°C higher) but costs 20-30% more, has higher mold shrinkage, poorer surface finish when unreinforced, and similar processing window. In 60% of typical general-engineering applications, PA6 (especially reinforced with 30-35% GF) delivers 90% of PA66's structural performance at a significantly lower material cost. PA66 is only justified when temperatures exceed 150°C continuous, you need the absolute maximum mechanical loading, or your company's design/quality standards are historically PA66-based.
Sometimes — it depends mostly on shrinkage and dimensional tolerance. 30% GF reinforced PA6 has ~0.35 % flow-direction shrinkage vs 0.30 % for 30% GF PA66 (cross-direction 0.95 % vs 0.90 %), so parts will be SLIGHTLY larger — about 0.02–0.05 mm for every 100 mm dimension. For snap fits, clearance fits, press fits and tight-dimension features (bore diameters, locating pins) the small size shift usually requires mold rework or core/sleeve inserts. For open non-structural housings or less-tight-tolerance brackets, direct switch with drying and temperature profile adjustment (lower melt for PA6) often works. Always run a single-cavity molding trial and CMM dimension check before committing to production.
PA6 absorbs slightly more moisture than PA66: equilibrium at 23°C / 50% RH is approximately 2.8–3.2 % for PA6 vs 2.5–2.8 % for PA66 (unreinforced). With 30% GF reinforcement, both drop proportionally: PA6 GF30 ~ 1.0 %, PA66 GF30 ~ 0.9 %. In practical terms, both need the same pre-drying process (80°C × 4h to < 0.08%) before molding — there is no meaningful difference in drying requirement.
As of mid-2026 spot pricing (EXW China): Unreinforced premium PA6 ~ USD 2.10–2.40/kg vs unreinforced premium PA66 ~ USD 2.60–3.00/kg → PA66 premium of ~25–30 %. For 30% GF reinforced grades: PA6 GF30 ~ USD 1.95–2.25/kg vs PA66 GF30 ~ USD 2.45–2.85/kg → similar 22–28 % gap. For cost-optimized-based GF grades the percentage gap is similar but absolute gap per kg is smaller (~ USD 0.35–0.45). Oil price swings and upstream adiponitrile (PA66 monomer) supply squeezes can temporarily widen the premium to 40–50%.
Peak of 140°C, continuous exposure under 120°C? PA6 GF30 has HDT of ~190°C at 1.82 MPa — so both PA6 GF30 and PA66 GF30 pass from a heat-deflection standpoint. The decision is about CREEP and long-term heat-aging. If the bracket is structural (bolted pre-load, fatigue vibration cycles) and needs 5,000+ hour life at 120°C+, choose PA66 GF30 or PA6/66 copolymer blend for better long-term retention. If it's a light-load clip, housing or guide and peak temperature is transitory (warm-up spikes only), PA6 GF30 is a cost-effective choice that meets 99% of under-hood non-safety brackets. Juhai offers a 10,000 hour heat-aging test on sample brackets if you want definitive evidence for your specific geometry.
PA6 GF generally gives slightly better (smoother, less-fibrous) surface appearance than PA66 GF at the same GF% and mold temperature. Reason: PA6 has lower melt viscosity and better wet-out of glass fibers as it flows, so the polymer 'skin' layer on the mold surface is thicker. With proper 80–95°C mold temperature, correct gate location and optimized first-stage injection velocity, PA6 GF30 can achieve a class-B paintable surface without secondary operation. PA66 GF30 at same mold temperature will often show micro-floating fiber (matte / 'orange peel' texture) unless you use higher mold temperature 90–110°C, mold temperature variotherm or special cosmetic additives. If you are painting or plating the part anyway, choose PA6 for easier surface prep.
Because PA6 and PA66 are both polyamides and chemically similar, you CAN switch between them without full screw disassembly — but you MUST run a proper transition purging step. Transition procedure: 1) Empty hopper of previous material. 2) Run 3–5 shots of unfilled PA6 natural (cheaper purge) at 25–30°C higher than normal PA6 temperature. 3) If switching from PA66 to a colored PA6, run 2 more shots of the target color's natural base. 4) Charge new material. Skipping the purge results in unmelted PA66 'fish-eyes' in PA6 parts because PA66's 40°C-higher melting point means residual PA66 pellets won't fully melt at PA6 processing temperature.
Yes, this is exactly what a PA6/66 copolymer or alloy product does, and it is one of the most useful compromises in modified engineering plastics. Our ETF02 High-Temperature Nylon grade is a PA6/PA66 blend: you get ~90% of PA66's HDT (210°C) with much better PA6-style surface finish and flow, at a price point about 10% above PA6 — not the full 25% PA66 premium. Copolymer blending is also an excellent way to solve warpage issues on parts where pure PA66 is too stiff and shrinks unevenly.
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.
Free Grade Recommendation for Your Part
Send us your part drawing, load condition, temperature range and annual volume — our R&D engineers will recommend either PA6, PA66 or a copolymer blend, with expected mechanicals and two pricing options (premium and cost-optimized grades).
Contact Juhai R&D →
