PA6 vs PA66 vs PA12 vs PA11: Choosing the Right Nylon Grade

"Nylon" Is a Family, Not a Material

Nylon is the common name for polyamides (PA): polymers whose chains are linked by amide groups. The number after "PA" tells you how many carbon atoms sit in the repeating units of the chain, and that single number predicts most of how a grade behaves. Short chains (PA6, PA66) pack more amide groups per length. Amide groups are what make nylon strong and heat-resistant, but they are also what grab water from the air. Long chains (PA11, PA12) have fewer of them, so they are a little less strong but far more stable and chemically resistant. Almost every trade-off in this article follows from that one fact.

The Grades at a Glance

Typical values for printed parts in the XY direction, dry as printed. Exact figures vary by supplier, so treat them as a comparison, not a specification.

PA6: The Tough Default

PA6 is the original engineering nylon and the toughest unfilled grade. It has the best fatigue and impact resistance of the family, which is why it is used for snap-fits, hinges, gears and anything that gets hit or flexed repeatedly. Its weakness is water: PA6 can absorb around 2.5-3% of its weight from humid air at equilibrium (more when soaked). As it does, it gets tougher and more flexible, but it also loses stiffness and grows by a few tenths of a percent. That is fine for a bracket and a problem for a bearing fit. Choose PA6 when toughness matters more than holding a tight dimension.

PA66: When It Has to Take Heat

PA66 has a similar chemistry to PA6 but a more regular chain that crystallizes harder. The result is a melting point about 40 °C higher, higher stiffness, and better strength at elevated temperature. It absorbs about as much moisture as PA6. PA66 is also the grade most injection-molded nylon parts are made from (think automotive clips, cable ties, power-tool housings), so if you are prototyping a part that will later be molded in PA66, printing in PA66 gives you the closest behavior. The cost is printability: PA66 shrinks and warps more, so it takes more care and is priced a little higher.

PA6/66 Copolymer: The Practical Compromise

Mixing PA6 and PA66 units in one chain disrupts crystallization. That sounds like a downside, but it means the material shrinks less as it cools, so parts warp far less. CoPA keeps most of nylon's toughness and heat resistance and is the most forgiving nylon for large parts and flat plates, which are exactly the geometries that curl off the bed in pure PA6 or PA66. If your part is big and you just need "nylon", CoPA is often the right answer.

PA12: Stable, Precise, Chemical-Proof

PA12 has twelve carbons per repeat unit, so far fewer amide groups. It absorbs roughly a third as much moisture as PA6, which means its dimensions and stiffness hardly change between a dry winter and a humid summer. It also resists fuels, oils, greases and many solvents better than the short-chain nylons, and it has low friction. The trade-off is somewhat lower strength and heat resistance. PA12 is the grade to pick for precise functional parts: fittings, fluid-handling parts, sliding components and anything with a fit that must hold. It is also the dominant material in SLS powder printing, so a printed PA12 part is a good stand-in for an SLS production part.

PA11: PA12's Tougher, Bio-Based Cousin

PA11 is made from castor oil rather than petroleum. Chemically it sits right next to PA12, with similarly low moisture uptake and excellent chemical resistance, but it stretches further before breaking and keeps its impact strength at low temperatures where PA12 turns brittle. Choose PA11 over PA12 when a part has to bend, survive drops, or work in the cold, or when you have a renewable-content requirement.

PPA and PAHT: The High-Temperature End

Polyphthalamide (PPA) builds rigid aromatic rings into the nylon chain. That raises heat resistance dramatically and cuts moisture sensitivity, at the price of a much harder print (very high temperatures and a heated chamber). High-temperature nylons like PAHT follow the same idea. These grades are almost always printed with carbon fiber (PPA-CF, PAHT-CF), and they are the choice for parts that live near engines, motors or hot fluids, where a standard nylon would soften.

Adding Fiber: -CF and -GF Grades

Chopped fiber turns a tough nylon into a stiff one. The fibers carry load, reduce creep, and physically restrain the swelling that moisture causes, so a reinforced nylon holds its shape much better than the same base unfilled. What changes with the fiber:

• Carbon fiber (PA6-CF, PA12-CF, PA11-CF, PA612-CF, PPA-CF): the highest stiffness for the weight and a matte black finish. Carbon conducts electricity and blocks radio signals, so it is a poor choice for antenna housings.
• Glass fiber (PA6-GF): somewhat less stiff than CF but more impact-tolerant, electrically insulating and RF-transparent. Often the better pick for electronics enclosures and anything that gets knocked around.
• What fiber costs you: elongation. A reinforced nylon bends much less before it breaks, so snap-fits and living hinges should stay in unfilled PA6 or PA11.
• Base grade still matters: PA6-CF is the strongest mainstream nylon composite; PA12-CF is the most dimensionally stable in humid conditions; PA11-CF is the least brittle; PA612-CF sits between PA6-CF and PA12-CF.

Which Grade Should You Choose?

Start from the property that would make the part fail, then pick the grade that is strongest in it:

Designing for Nylon's Moisture Behavior

Whatever grade you choose, remember that nylon parts come out of our printers dry and then equilibrate with the air around them over days to weeks. For PA6 and PA66 that means a small gain in toughness, a small loss in stiffness and slight growth. Leave 0.1-0.2 mm of extra running clearance on gears and bushings in short-chain nylons, or move to PA12, PA12-CF or PET-CF when a fit is critical. Unfilled nylon's strength comes more from geometry than from stiffness, so ribs and 2-3 mm walls beat solid infill.

Quote It in the Grade You Need

Every grade in this article is selectable on the quote page: upload your file, choose FDM, and pick PA6, PA66, PA6/66 (CoPA), PA12, PA11 or one of the fiber-reinforced grades. The price updates for your exact geometry. If you're not sure which grade fits, choose the closest one and describe the load, temperature and environment in your order notes; our engineers will confirm or suggest a better grade before anything prints.