PA12 vs PA66: Long-Chain vs Standard Nylon — Which One Should You Choose?
A five-dimensional comparison of moisture absorption, dimensional stability, heat resistance, chemical resistance and cost — with typical applications and a quick selection guide
Within the nylon (polyamide) family, PA66 is the most widely used general-purpose engineering nylon, while PA12 is the long-chain nylon renowned for low moisture absorption and high dimensional stability. Both are called "nylon", yet their performance orientations are fundamentally different: PA66 balances strength and heat resistance as the workhorse for structural parts, while PA12 is virtually irreplaceable in fuel lines, medical catheters and precision gears. The cost of choosing wrong is very real — out-of-tolerance dimensions causing assembly failures, leaking fuel lines, or brittle fracture in cold climates, any of which can trigger batch returns or even safety incidents. This article systematically compares the real-world performance of PA12 and PA66 across five key dimensions and provides an application-based selection quick guide. Note: material prices mentioned are for reference only and fluctuate with the market.
PA12: The Low-Absorption, Dimensionally Stable Long-Chain Nylon
PA12 (Nylon 12) is produced by ring-opening polymerization of laurolactam. With one amide group per 12 carbon atoms, it has the lowest amide density and the longest carbon chain among commercial nylons. This "long-chain" structure delivers three defining traits: first, extremely low moisture absorption (~1.5% at saturation, roughly 1/5 of PA66), so molded parts barely change dimension with ambient humidity; second, the long carbon segments between amide groups make the chains flexible, giving excellent low-temperature impact toughness with no brittle fracture at -40°C; third, outstanding resistance to non-polar media such as gasoline, diesel, hydraulic oils and brake fluids. PA12 also has a density of only ~1.01 g/cm³ — the lightest of common nylons. Its weaknesses are equally clear: a melting point of ~178°C and a low heat deflection temperature rule out hot service, and its 55–65 MPa tensile strength trails PA66. Typical PA12 applications concentrate on automotive fuel and vacuum lines, pneumatic brake tubing, medical catheters, fiber-optic cable jackets, precision gears and SLS 3D-printing powder.
PA66: The Strong, Heat-Resistant Workhorse of Engineering Nylons
PA66 (Nylon 66) is made by polycondensation of hexamethylenediamine and adipic acid — the "66" refers to the six carbon atoms in each monomer. Its high amide density creates strong hydrogen bonding, giving PA66 leading mechanical performance in the nylon family: 75–85 MPa tensile strength dry-as-molded, rising to 170–190 MPa with 30% glass fiber; a melting point of ~260°C, with GF30 grades reaching an HDT near 250°C for sustained under-hood service. PA66 also has the most mature modification ecosystem — glass reinforcement, flame retardancy (UL94 V-0), toughening, wear resistance (PTFE/MoS₂) and hydrolysis resistance are all readily available, with ample supply and rich grade options. The price paid is higher moisture absorption (~2.5% at equilibrium, up to 8% at saturation): parts swell and stiffen less after moisture uptake, so precision parts need conditioning or design allowance. It also resists neither strong acids nor road de-icing salts (calcium chloride) — salt-exposed service demands hydrolysis-resistant grades. PA66 is widely used in engine covers, radiator end tanks, electronic connectors, power-tool housings, industrial gears, cable ties and sports equipment.
Quick Comparison
| Property | PA12: The Low-Absorption, Dimensionally Stable Long-Chain Nylon | PA66: The Strong, Heat-Resistant Workhorse of Engineering Nylons |
|---|---|---|
| Moisture Absorption & Dimensional Stability | PA12 absorbs only ~1.5% moisture at saturation (~0.5% equilibrium at 23°C/50% RH) — the lowest among common nylons. Molded parts barely change dimension with ambient humidity and need no conditioning, ideal for dimension-sensitive snaps, gears and optical structural parts. | PA66 absorbs ~2.5% moisture at equilibrium, up to 8% at saturation. Parts swell ~1–2% and lose stiffness after moisture uptake — precision fits need conditioning allowance or glass-fiber grades to restrain hygral expansion. |
| Mechanical Strength | PA12 offers ~55–65 MPa tensile strength and ~1200–1700 MPa flexural modulus — modest among nylons — but with good toughness, low notch sensitivity and excellent flex fatigue resistance. 30% glass-filled PA12 raises tensile strength to 110–130 MPa. | PA66 delivers 75–85 MPa tensile strength and ~2800 MPa flexural modulus dry-as-molded; with 30% glass fiber, tensile reaches 170–190 MPa and modulus exceeds 9000 MPa — the strength benchmark for structural nylon parts. |
| Heat Resistance | PA12 melts at ~178°C with an HDT of ~55°C at 1.8 MPa; keep continuous service at ≤80°C. Not suited to under-hood or heat-generating appliance interiors. | PA66 melts at ~260°C with an unreinforced HDT of 70–85°C; 30% glass fiber raises HDT to ~250°C. Heat-stabilized grades run continuously at 120–150°C — the standard for under-hood components. |
| Chemical Resistance (Fuels & Oils) | PA12 resists gasoline, diesel, hydraulic oils, brake fluids and refrigerants exceptionally well — no swelling or embrittlement in long-term contact. The standard material for fuel lines, vacuum and pneumatic tubing, and fuel filters. | PA66 handles engine oils and greases well but is attacked by strong acids, phenols and road de-icing salts (calcium chloride); parts in long-term salt exposure need hydrolysis-resistant grades or they embrittle by hydrolysis. |
| Low-Temperature Toughness | PA12 stays ductile below -60°C and retains good impact toughness at -40°C — a reliable choice for outdoor parts, air tubing, cable jackets and ski-equipment components in cold climates. | PA66 is brittle at low temperatures in dry state (moisture conditioning plasticizes and helps); for severe cold choose toughened PA66 (POE/EPDM modified), which multiplies -30°C impact resistance several-fold. |
| Processing & Molding | PA12 still needs drying before molding (80°C/4–6 h). It flows well, with ~0.5–1.5% molding shrinkage and good isotropy, filling thin-wall long-flow parts easily; it is also used in SLS 3D printing. | PA66 is hygroscopic and must be thoroughly dried (80–90°C, 4+ hours) or splay and bubbles appear. Shrinkage is 1–2% and notably anisotropic — mold design must account for orientation warpage. |
| Cost & Availability | PA12 costs roughly 2–3× PA66, with global capacity concentrated among few suppliers and relatively tight supply. Reserve it for genuine performance needs (fuel systems, medical, precision parts), not cost-driven general use. | PA66 offers excellent cost-performance, ample supply from many vendors and a mature modification ecosystem — the first choice for high-volume structural parts. Pricing follows adiponitrile feedstock cycles, so watch market windows. |
Test with Real Samples — Let Data Decide
Free 5–10 kg samples + full TDS, response within 24 hours
Recommendation
Selection guidance (application quick guide): ① Fuel systems (fuel lines, fuel filters, tank components), hydraulic/pneumatic tubing → PA12; ② Medical catheters, infusion lines, minimally-invasive instrument parts → PA12 (medical grades require biocompatibility certification); ③ Dimension-sensitive precision gears, snaps and optical structural parts → PA12 or glass-filled PA12; ④ Cold-climate outdoor parts, cable jackets, air tubing → PA12; ⑤ Under-hood components, radiator end tanks, high-temperature electrical parts → PA66 (GF30/heat-stabilized); ⑥ Electronic connectors, power-tool housings, industrial gears, cable ties → PA66 (FR/toughened/wear-resistant modifications as needed); ⑦ Where both strength and low moisture uptake matter → glass-filled PA66, or evaluate middle-ground options such as PA612 or MXD6. Jinsu supplies modified PA66 (GF30/FR/toughened/wear-resistant/hydrolysis-resistant) and long-chain nylon series, with TDS and free 5–10 kg samples for validation.
Conclusion
PA12 and PA66 are not simple substitutes — each owns its own application territory: PA12 wins on dimensional stability, media resistance and low-temperature toughness; PA66 wins on strength, heat resistance and cost. The key to selection is laying out your service conditions clearly — operating temperature, media contact, dimensional precision requirements, load type and volume cost targets — and the answer becomes obvious. If you are torn between the two, or worried about PA66 moisture uptake yet priced out of PA12, send us your drawing or operating conditions. Jinsu's technical team will match the exact grade (including reinforced/FR/hydrolysis-resistant options) and arrange free sample testing — let the data decide.
Frequently Asked Questions
Can PA12 directly replace PA66?
Direct replacement is not recommended. PA12 has lower tensile strength, stiffness and heat resistance than PA66 — structural or hot parts may fail after substitution. Conversely, PA66 cannot replace PA12 in fuel lines or precision-dimension parts, where moisture swelling risks leakage and tolerance loss. Always verify load, temperature and media conditions item by item before any substitution.
Why is PA12 so much more expensive than PA66?
PA12's feedstock laurolactam has a long synthesis route and high technical barriers, with global capacity concentrated among a few chemical giants and little supply elasticity; PA66's adiponitrile/hexamethylenediamine chain is mature and high-capacity. PA12 therefore costs 2–3× PA66, with tighter supply during market swings.
Which nylon should be used for fuel lines?
PA12 is the first choice. It has long-term validation against gasoline, diesel, biodiesel blends and brake fluids, and is the automotive standard for fuel lines — often serving as barrier or outer layer in multilayer tubing. PA66 lacks sufficient fuel resistance and is not recommended for fuel delivery lines.
PA12 or PA66 for SLS 3D printing?
PA12 powder dominates SLS 3D printing: wide sintering window, low warpage, low moisture uptake, good surface quality and detail resolution — ideal for functional prototypes and small batch parts. PA66 powder needs higher sintering temperatures with a narrow window and is rarely used. For heat-resistant printed parts, consider PA11 or modified powders.
Is there a middle ground between moisture absorption and strength?
Yes. ① Glass-filled PA66: glass restrains hygral expansion and boosts strength — the most common compromise; ② PA612: a long-chain nylon with moisture uptake between PA12 and PA66 at moderate price; ③ MXD6: a high-barrier semi-aromatic nylon with low absorption and high stiffness for precision structural parts. Ask your supplier to recommend based on budget and performance needs.
Still torn between two materials?
Send us your drawing or service conditions — our technical team will match the right grade and arrange free sample testing.
Jinsu New Material
WhatsApp: +86 173 5113 2569
sales@maxnmtech.com