PLA-CF Carbon-fiber-filled polylactic acid (PLA-CF)

PLA-CF is ordinary PLA, the easy-to-print, plant-derived plastic, filled with short chopped carbon fibers. QIDI describes its version as chopped carbon fiber reinforced PLA. The fibers are tiny fragments mixed through the plastic like fine aggregate; they are not the continuous woven or unidirectional carbon fiber you see in bicycle frames and race-car panels, and a PLA-CF part is not a carbon-fiber composite in that sense.

What the fibers do is make the plastic much stiffer and more dimensionally stable, and they give the surface a fine, matte, slightly textured look that hides layer lines and reads as premium. QIDI's comparison table lists a bending strength of 91.57 MPa for PLA-CF in the XY plane against 61.29 MPa for its PLA Basic, so for flat, plate-like parts loaded in bending the improvement is real.

What the fibers don't do is change PLA's heat behavior. QIDI lists the heat deflection temperature (HDT, the temperature at which a loaded test bar bends a set amount) at 55.2 °C at 0.45 MPa, essentially identical to PLA Basic at 55.3 °C. If a PLA part would sag in a hot car, a PLA-CF part will too.

Fiber-filled filaments are abrasive and wear ordinary brass nozzles quickly, so we print PLA-CF only with hardened nozzles; the stock bimetal nozzles on our QIDI Max4 and Plus5 are rated by QIDI for fiber-filled filaments, and we never use the optional 0.2 mm stainless nozzle for it. The fibers also make PLA-CF more sensitive to moisture during printing, so we dry it before each job.

Stiffness is the reason to buy PLA-CF. Short fibers increase the material's resistance to bending, which QIDI's bending-strength figures reflect (91.57 MPa versus 61.29 MPa for PLA Basic in XY). For a bracket or a long thin arm, that means noticeably less deflection under the same load, or the option to use thinner sections for the same stiffness.

That stiffness comes with brittleness. Fibers reduce the plastic's ability to stretch before breaking, so PLA-CF parts tend to fail suddenly with a crack rather than bending first. In our ratings it scores low on impact. For parts that may be dropped, struck, or flexed in use (living hinges, snap-fits, clips), PETG or nylon is usually a better choice.

Like all FDM parts, PLA-CF is weaker between layers than along them, a property called anisotropy. Fibers align along the printed lines, which helps in-plane stiffness but does nothing for bonding between layers; QIDI's Z-direction tensile strength for PLA-CF is 24.09 MPa against 32.46 MPa for PLA Basic. We orient parts so the main loads run along the layers, and we'll flag any design where a key load pulls layers apart.

PLA in general creeps (slowly deforms) under sustained load, and the fibers reduce this somewhat by stiffening the matrix, but they don't remove it. A PLA-CF shelf bracket holding a steady weight, especially in a warm room, can still sag over months. For sustained loads, consider PETG-CF or a nylon composite.

PLA-CF is in our lowest heat band, the same as plain PLA. QIDI's table gives an HDT of 55.2 °C at 0.45 MPa, which is presumably as printed, since QIDI lists annealing separately and doesn't publish an annealed HDT. In practical terms, plan on PLA-CF parts starting to soften and creep in conditions that feel only “hot”, not extreme.

QIDI lists annealing (controlled baking after printing) at 70–80 °C for 4–6 hours as optional for PLA-CF. Annealing can raise PLA's heat tolerance by increasing crystallinity, but it also causes shrinkage, warping and dimensional change, and QIDI doesn't publish how much heat resistance PLA-CF gains. We anneal only by agreement, after a test piece, and we'd rather point you to an inherently heat-resistant material such as PETG-CF or ASA-CF.

PLA-CF is generally used indoors. PLA isn't formulated for long UV exposure, and over months in sunlight the surface can fade or turn chalky and the part can become more brittle. The black, fiber-filled surface tends to hide fading better than light colors, but the bigger problem outdoors is heat, which softens PLA long before UV damage shows. For outdoor service, choose ASA-CF.

PLA-CF's chemical resistance is essentially that of PLA, because the fibers don't protect the plastic. PLA generally tolerates water, mild soaps and brief contact with isopropyl alcohol, but solvents such as acetone, many paint thinners and some cleaning agents can soften or craze it, and fuels and brake fluid are not recommended.

If your part will see oils, fuels or cleaning chemicals, tell us the product names; nylon composites (PA-CF) are generally far more chemically resistant. For anything critical we suggest a soak test on a sample.

Finished PLA-CF parts absorb very little water: QIDI lists 0.3 % saturated water absorption, half the 0.6 % of its PLA Basic. That means printed parts stay dimensionally stable in normal humidity.

The filament is a different story. QIDI marks drying as required: damp PLA-CF oozes, extrudes bubbles and prints a rough surface. We dry it at QIDI's recommended 50 °C for 4–6 hours before printing and store it sealed, so this affects our process, not your part.

PLA-CF's main cosmetic appeal is its matte, faintly textured surface that hides layer lines much better than glossy PLA. Large flat faces look clean and uniform, and black PLA-CF reads as a premium, technical material in product photos and on the desk.

The bottom face takes on the texture of the build plate (smooth or textured PEI), and supported overhangs leave a rougher underside. Fine text and very small features are slightly softer than in unfilled PLA. The surface can mark if rubbed hard, and scratches show as lighter lines on dark colors.

Light sanding can blend support marks, but sanding through the surface exposes fibers and changes the sheen, so we prefer to orient parts to keep visible faces clean. PLA-CF can be primed and painted, though most customers choose it precisely to avoid painting. Vapour smoothing is not something we offer for this material.

Annealing is optional per QIDI (70–80 °C for 4–6 hours), with the trade-offs of shrinkage and possible warping; we do it only by agreement after a test. Heat-set inserts work well in PLA-CF and are our preferred way to add durable threads; tapped threads are acceptable for light, occasional use, and printed threads suit coarse sizes only.

PLA-CF is one of the more dimensionally stable materials we print. The fibers reduce shrinkage and warping, so long, flat parts stay flat and features land close to the CAD model. As with all FDM, small holes print slightly undersized, so we suggest modelling holes a little oversize or reaming them after printing.

Because PLA-CF is stiff and brittle, interference fits have little forgiveness: an overly tight press fit can split a boss rather than stretch around a pin. Design press fits with less interference than you would use for PETG, and use slip fits plus a fastener where you can.