PA6 vs PA12: Complete Comparison for Engineering Applications
Compare nylon 6 and nylon 12 on moisture absorption, dimensional stability, chemical resistance, cost, and which applications each material suits best.
PA6 and PA12 are two of the most widely used polyamide (nylon) grades in engineering. Both offer excellent mechanical strength and wear resistance, but they differ fundamentally in moisture absorption, dimensional stability, and price. Understanding these differences is critical when selecting a material for automotive fuel lines, pneumatic tubing, cable sheathing, or precision gears.
Key Differences at a Glance
The fundamental difference lies in the carbon chain length. PA6 has 6 carbon atoms per repeat unit, while PA12 has 12. Longer chains mean fewer amide groups, which translates to:
- PA6: absorbs up to 9.5% moisture at saturation; tensile strength ~70-85 MPa; melting point ~220°C. - PA12: absorbs only ~1.5% moisture; tensile strength ~50-60 MPa; melting point ~178°C.
Because PA12 absorbs far less water, its dimensions and mechanical properties stay stable regardless of humidity. PA6 is stronger and stiffer but changes dimension and properties as it absorbs moisture.
Moisture Absorption & Dimensional Stability
This is the single most important difference for precision applications. PA6 at 50% RH absorbs ~2.5-3% moisture, causing measurable dimensional growth and a drop in stiffness. A PA6 gear machined to tolerance may change dimensions after months in a humid environment.
PA12 absorbs only ~0.7-0.9% at 50% RH. Parts hold their dimensions and mechanical properties much better over time. For this reason, PA12 is preferred for:
- Pneumatic fittings and tubing (exposed to moisture and pressure) - Precision gears and bearings in humid environments - Cable and hose sheathing where kink resistance and flexibility matter
Chemical Resistance & Low-Temperature Performance
PA12's longer carbon chains give it superior resistance to many chemicals:
- PA12 resists fuels, oils, and greases exceptionally well, making it the standard choice for automotive fuel lines and brake lines. - PA12 has better low-temperature impact strength (down to -40°C), while PA6 becomes brittle at low temperatures. - PA6 offers better resistance to hot water and alkalis than PA12.
If your application involves fuel contact, low temperature, or outdoor weathering, PA12 is the safer choice. For hot water plumbing or alkaline environments, PA6 may perform better.
Cost & When to Choose Each
PA6 is significantly cheaper (roughly 40-60% lower cost than PA12) and offers higher strength, stiffness, and heat resistance. PA12 costs more because the monomer (lauryl lactam) is more expensive to produce.
Choose PA6 when: - Cost matters and parts are thick-walled or enclosed (moisture has limited effect) - You need maximum strength, stiffness, or HDT - Parts are reinforced with glass fiber (PA6-GF30 is very cost-effective)
Choose PA12 when: - Dimensional precision must hold in humid environments - Fuel/oil contact is involved - Low-temperature toughness is required - The part is thin-walled and exposed to the environment
Conclusion
PA6 and PA12 serve different engineering needs. PA6 is the cost-effective workhorse: strong, stiff, and heat-resistant, ideal for glass-filled structural parts where moisture exposure is limited. PA12 is the specialist: dimensionally stable, chemical-resistant, and tough at low temperatures, ideal for fuel lines, pneumatic systems, and precision parts in humid environments. Match the material to the environment, not just the price tag. Jinsu supplies both PA6 and PA12 grades with full technical support.
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