PA-CF Carbon-fiber-reinforced nylon 12 (PA12-CF)

PA12-CF is nylon 12 filled with short chopped carbon fibers. Nylon 12 is one of the more dimensionally stable nylons, absorbing less water than PA6, and the carbon fiber makes it much stiffer and helps it resist warping. The result is a light, stiff, tough material with a dark matte finish that has become a workhorse for functional engineering parts in FDM.

The grade we print is QIDI PA12-CF. QIDI markets it for strength, stiffness, thermal resistance and wear, and says the fiber network relieves internal stress during printing for good dimensional stability. At 1.09 g/cm³ it is one of the lightest engineering filaments, which matters for drones, robots and anything that moves.

Carbon fiber is abrasive. It wears soft brass nozzles quickly, so it needs a hardened nozzle; our printers' stock 0.4 mm bimetal nozzles are rated by QIDI for fiber filaments, but QIDI says the 0.2 mm nozzle is not compatible. Practically, that means the finest detail we can offer in PA12-CF is set by a 0.4 mm nozzle.

A key point for buyers: PA12-CF is anisotropic, which means its properties depend on direction. The fibers line up along the direction the nozzle travels, so a part is much stiffer and stronger along its printed lines than across them, and weakest between layers. Telling us how your part is loaded is more important with this material than almost any other.

Carbon fiber's main contribution is stiffness. PA12-CF's bending modulus of about 3.9 GPa as printed, and 4305 MPa annealed per QIDI's comparison table, is far above unfilled nylon 12, so parts deflect less under load. QIDI's guide lists bending strength of 124.07 MPa in the XY direction, while the product page lists 114.12 MPa; the guide figure appears to be for annealed parts. We use the lower number for design.

The trade-off is ductility. Elongation at break is only about 1.6%, so PA12-CF breaks rather than bends when overloaded. Its impact strength of 10.01 kJ/m² is decent for a fiber-filled material, but it doesn't have the forgiving, yielding behavior of unfilled nylon.

Anisotropy is significant. QIDI lists tensile strength of 76.95 MPa in the XY plane and 38.61 MPa in Z, about half, so the bond between layers is the weak link. Within each layer, the fibers align along the toolpath, so even XY strength depends on whether loads run along or across the printed lines. We orient parts so the main load runs along the layers and, where possible, along the perimeters.

Infill matters more with fiber-filled parts than with unfilled ones, because much of the stiffness comes from solid perimeters and top and bottom skins where fibers run in long continuous lines. For stiff brackets we generally add perimeters and solid layers rather than just raising infill density. If weight is critical, tell us, and we'll balance stiffness against mass.

Fiber-filled nylon creeps less than unfilled nylon under steady load, which makes it better for bolted brackets and clamps. Use metal inserts for bolted joints and spread loads with washers, because the material can still crack around a point load.

HDT, the heat deflection temperature, is the temperature at which a test bar bends a set amount under a fixed load. For PA12-CF the difference between as-printed and annealed parts is huge. QIDI's product page lists 78.4 °C for unannealed parts (load not stated), while its comparison data shows 138.2 °C at 0.45 MPa after annealing.

In plain terms: an as-printed PA12-CF part handles heat about like PETG, while an annealed part handles much more. If your part needs that heat resistance, you need annealing, which we do only by agreement. The melting point is 167 °C, so even annealed parts should be kept well below that.

Annealing means heating the finished part in an oven so the nylon crystallizes more fully. QIDI's guide specifies 100 °C for 8 hours, and the product page 80–100 °C for 4–6 hours. The fibers limit shrinkage, but parts can still change size slightly or distort, so we anneal a test piece first and measure it.

The carbon content makes PA12-CF black and gives reasonable UV protection compared with natural nylon. Over long sun exposure the matte surface can fade, chalk lightly and expose more fiber. A UV-resistant coating extends life outdoors.

Water and humidity are more of a concern than UV. Nylon 12 absorbs less than PA6, but QIDI still lists saturated water absorption of 2.46% for PA12-CF, so outdoor parts swell and soften slightly in wet weather.

Like other nylons, PA12-CF generally resists oils, greases, fuels including gasoline and diesel, and many solvents such as isopropyl alcohol and acetone. Nylon 12 is generally more resistant than PA6 to many chemicals and to salt solutions such as road salt.

Strong acids and oxidizers such as concentrated bleach generally attack nylon. Hot water over time also degrades it. Test a sample if your part will sit in a specific fluid, especially at elevated temperature.

PA12-CF is hygroscopic, meaning it absorbs water from the air. Wet filament prints with bubbles, rough surfaces and weak layers, so we dry it at 80–100 °C for 4–6 hours and print from sealed storage below 15% RH, as QIDI requires.

Finished parts also take on moisture until they reach equilibrium with the air. QIDI lists saturated water absorption of 2.46%, slightly more than its UltraPA nylon. As a nylon part absorbs water, it becomes tougher but less stiff and grows slightly; QIDI says PA12-CF keeps strong tensile and flexural strength in both wet and dry conditions, but you should still expect some change. If dimensions or stiffness are critical in humid conditions, consider PET-CF.

PA12-CF has a dark, matte, slightly textured finish that hides layer lines well and looks technical and premium. It's popular for visible parts in robotics and products for that reason.

Surface texture is uniform, but you may see faint fiber sheen at certain angles and slightly rougher supported faces. Color is generally black only.

PA12-CF sands better than unfilled nylon, though sanding can expose fibers and leave a slightly fuzzy feel. Wear a mask; carbon dust is an irritant. It machines, drills and taps cleanly, and heat-set inserts install well.

Vapor smoothing isn't something we offer for this material. Annealing is the main post-process and is done only by agreement.

Painting is possible with suitable primers, but most clients prefer the natural matte black finish.

Carbon fiber reduces shrinkage and warping compared with unfilled nylon, so PA12-CF holds dimensions well and large flat parts are much more practical. Expect better accuracy than unfilled nylon but slightly more variation than PLA.

Holes print slightly undersized, as with all FDM parts. PA12-CF drills and reams cleanly, so we recommend designing precise bores slightly undersized and finishing them.

Annealing can change dimensions slightly; plan critical fits after annealing, or let us anneal a test piece first. Moisture uptake also changes size slightly over time.