Every filament here is a base polymer with something solid stirred into it that does not melt. That is the only thing the family has in common — and it means a spool of carbon-filled PLA has far more in common with plain PLA than it does with carbon-filled nylon.
Which leads to the one piece of advice this page exists to give: choose the base polymer first. Decide whether the part needs PLA's ease, a copolyester's weather resistance, a styrenic's heat tolerance or a polyamide's toughness, and only then ask whether the filled version of that polymer is worth its price. Almost everyone does this backwards, buying "carbon fibre" as though it were a material and then discovering the base polymer underneath it still softens at 55 °C.
| Material | Base polymer | The filler is bought for |
|---|---|---|
| PLA-CF | PLA | rigidity and flat plates, on a machine needing no enclosure |
| PETG-CF | PETG | less stringing, less droop, and a part that leaves the plate willingly |
| ABS-CF | ABS | halved warping, which is what makes a large panel possible |
| PA6-CF | PA6 | turning an unprintable nylon into an engineering material |
| PA6-GF | PA6 | impact resistance and electrical insulation |
| Metal-filled PLA | PLA | appearance, mass and a surface that polishes like metal |
What every fibre-filled member gains
Dimensional stability. Shrinkage drops in every fibre-filled grade — modestly in the easy base polymers, dramatically in the difficult ones. On several members of this family that reduction, rather than any mechanical property, is the actual reason the grade exists at all.
Stiffness. The modulus climbs, so parts deflect less under load.
A matte surface that hides layer lines, which is pleasant and also conceals under-extrusion, so calibrate on unfilled filament.
What every fibre-filled member loses
Impact resistance. Filled grades are more brittle than the polymers they are built on, without exception. There is a one-question test that resolves most of the choices on this page: did your prototype break, or did it bend? Breakage means stay unfilled. Bending means the filler is the fix.
Interlayer strength. Reinforcement is added in the plane of each layer and nowhere else, so a filled part is stronger in two directions and no stronger — often weaker — in the third. Part orientation therefore matters more on this shelf than anywhere else on this site, and it is the thing most worth getting right before any setting.
Tensile strength, usually unchanged. Stiffness and strength are separate properties, and it is stiffness that fibre buys. Buying a filled grade because you want a stronger part is the single most common mistake here.
Particle-filled is a different animal
Metal-filled grades belong to this family by construction and to none of it by behaviour. Spherical metal powder does not align, does not reinforce and carries no load — it is inert mass in a plastic binder. So the tensile figure goes down rather than sideways, the density goes up enormously, and what you gain is appearance, weight and a surface that takes a genuine metal polish.
Treat it as a decorative material with a structural ceiling, and never as a step toward printing metal.
The hardware tax, which applies to all of them
Hardened nozzles are mandatory, not advisable. Carbon fibre destroys brass in tens of hours; glass fibre and metal powder are harder still. The failure is quiet — a worn 0.4 mm orifice becomes a slightly larger, out-of-round one, and every dimension on every subsequent print is wrong while the settings on screen still look right.
Go up a nozzle size. Filler agglomerates bridge small orifices, so 0.6 mm is a comfortable default and anything below 0.4 mm is unusable.
Everything else wears too. Drive gears, filament guides and PTFE couplings all have a shortened life. Budget for it rather than discovering it.
Dry it, even when the base polymer would not need it. The filler and the filler–matrix interface hold moisture independently of the polymer, which is why fibre-filled PLA has a drying schedule and plain PLA does not.
Start with the base polymer
Work down the list: what does the part need thermally and chemically? That picks the base polymer. Then — does it need to stop bending, stop warping, or stop stringing? If yes, the filled grade is worth the nozzle and the money. If the honest answer is that the part needs to be stronger or tougher, stay unfilled.