Nylon (PA) Nylon (polyamide, PA): PA6, PA12, PA6/66 copolymers and QIDI UltraPA (PPA-based)

Nylon is the common name for polyamides (PA), a family of tough, slippery engineering plastics used for gears, bushings, cable ties, zip-ties and power-tool parts. The number after PA describes the chemistry: PA6 and PA66 are the classic, very tough grades that absorb the most water; PA12 absorbs noticeably less and is more dimensionally stable; PA6/66 copolymers are blends tuned to print with less warping. Whichever grade, nylon's defining traits are toughness, wear resistance and a strong appetite for moisture.

The unfilled nylon we stock is QIDI UltraPA, which QIDI describes as a modified high-temperature nylon on a PPA base. PPA, polyphthalamide, is a semi-aromatic polyamide: part of the molecule is a stiff ring structure, which raises stiffness and heat resistance and lowers water uptake compared with PA6. QIDI claims UltraPA's saturated moisture absorption is about one-fifth that of ordinary PA6. We can source PA6, PA12 or PA6/66 grades on request when a project calls for a specific chemistry.

Nylon is hard to print well. It warps, it needs a hot enclosed chamber, and wet filament prints with bubbles and rough, weak layers. Prusa's knowledge base calls it very hard to print and notes poorly stored filament can absorb up to 10% of its weight in water. That is why we dry it before printing and keep it sealed below 15% RH while it prints, as QIDI asks.

For buyers, nylon is the material to pick when a part must flex, slide, wear or take repeated impacts without cracking. It is not the stiffest or most heat-resistant option; for those, look at the carbon-fiber nylons PA-CF and PAHT-CF.

Nylon's headline is toughness. UltraPA's elongation at break of about 10% is several times that of the fiber-filled grades, so a nylon part bends and yields before it breaks, which is what you want for clips, hinges and parts that might be overloaded. Its bending modulus of about 3.2 GPa makes it stiffer than many unfilled nylons, a benefit of the PPA base.

Fatigue and wear are where nylon really pays off. A living hinge or snap-fit that would crack in PLA after a few dozen cycles can last much longer in nylon. Nylon is also naturally slippery, which QIDI describes as self-lubricating, so gears and bushings run quietly and wear slowly, especially against smooth metal.

Like all FDM parts, nylon is weaker between layers. QIDI lists UltraPA's tensile strength at 69.29 MPa along the layers and 50.03 MPa between them (Z), so a bend that peels layers apart is the weak case. For hinges especially, we orient the part so the hinge flexes along the layers, never across them.

Nylon creeps under steady load: a bolted joint or a clip held under strain will slowly relax, more so when warm or damp. For bolted joints, use metal inserts or washers to spread the load, and avoid designs that rely on a permanent interference fit to hold.

HDT, the heat deflection temperature, is the temperature at which a test bar bends a set amount under a fixed load. QIDI gives UltraPA 79.6 °C at 0.45 MPa in its guide and 72.5 °C (load not stated) on the product page. That places it between PETG and ABS for short-term heat, which surprises people who think of nylon as a high-temperature material.

Nylon's melting point is high, 231 °C for UltraPA, so it doesn't melt or drip when hot. What happens instead is that it softens and loses stiffness well below that, so lightly loaded parts survive warm environments while loaded parts sag. For heat under load, the annealed carbon- or glass-fiber nylons are a big step up.

QIDI lists optional annealing at 80–100 °C for 4–8 hours (the product page says 4–6 hours), which it says improves strength. Annealing can shrink and distort a part slightly, so we do it only by agreement and measure a test piece first.

Nylon has only fair UV resistance. In sunlight, surfaces generally yellow and become more brittle, and the effect is fastest on thin parts and light colors. Carbon-black pigment helps considerably.

Weather also means humidity. An outdoor nylon part will gain and lose moisture through the seasons, growing slightly in wet weather and shrinking in dry. That doesn't usually cause failure, but it does loosen or tighten fits.

Nylon is generally very resistant to oils, greases, fuels including gasoline and diesel, and many solvents, which is why it's used for fuel-line clips and engine parts in molded form. Isopropyl alcohol and acetone do not generally dissolve it. Brake fluid and most automotive fluids are generally tolerated.

Its weaknesses are strong acids, some strong bases and oxidizers such as concentrated bleach, which degrade polyamides. Hot water over long periods also slowly breaks nylon down. If your part will see a specific chemical, tell us so we can check compatibility, and test a sample.

Moisture is the defining issue with nylon. It is hygroscopic, meaning it pulls water from the air, and QIDI lists UltraPA's saturated water absorption at 2.1%, while ordinary PA6 absorbs more. Before printing, wet filament ruins parts: QIDI and Prusa both warn of bubbles and rough surfaces, so we dry it at 80–100 °C for 4–6 hours and print from sealed, desiccated storage below 15% RH.

After printing, your part keeps absorbing moisture from the air until it reaches equilibrium. That isn't just a problem; it changes properties. QIDI's wiki, quoted in its PAHT-CF guide, says nylon parts used in humid air or water gradually lose some strength and stiffness and become tougher. A freshly printed, bone-dry nylon part is at its stiffest and most brittle; after conditioning in normal air, it is more flexible and harder to break.

Moisture also means dimensional change. A part grows slightly as it absorbs water, which matters for close fits and precise bearings. If a dimension is critical, tell us, and consider having the part conditioned in normal room air for a few days before measuring it. For the most dimensionally stable nylon-like option, consider PAHT-CF, which absorbs less, or PET-CF, which absorbs much less.

Nylon prints with a slightly matte, waxy or silky surface depending on the grade, and it feels smooth to the touch. Layer lines are visible but softened. Natural nylon is translucent off-white; QIDI UltraPA and most engineering grades are supplied in black or neutral colors.

Fine features are slightly rounded, and nylon's tendency to string means small details may need a light cleanup. For crisp cosmetic models, PLA is better.

Nylon is hard to sand: it tends to fuzz rather than produce clean dust. Light trimming with a sharp blade and fine sanding work for cleanup. It is also difficult to paint without a suitable primer, and textile dyes are a classic way to color natural nylon parts.

Vapor smoothing is not something we offer for nylon. Annealing is done only by agreement, as described above. Heat-set inserts install very well in nylon because it reflows cleanly around them.

QIDI's PA guidance says to remove supports within 2 hours of printing, before the material absorbs moisture and the bond tightens. We handle that on our side.

Nylon shrinks more than PLA or PETG as it cools, and it warps, especially on long, flat parts. We print it enclosed with a heated chamber, on PEI with PVP glue, as QIDI recommends. Even so, expect slightly more variation than with rigid materials, and the dimensions will shift a little as the part absorbs moisture.

Holes print undersized, as with all FDM. Nylon reams and drills well, so for bearing bores and precise holes, we recommend designing them slightly undersized and finishing them to size.

For gears, make sure the module or pitch is not too fine; very small teeth soften at their tips. Send us the mating part or specification and we'll suggest an appropriate clearance.