Filled and specialty filaments

Beyond the everyday plastics is a shelf of filaments that trade easy printing for a specific superpower: stiffness that won't creep, dimensional stability that holds a jig true, a surface that survives rubbing, or a look that hides the fact it was printed at all. You reach for these when a standard material almost works but falls short on one hard requirement — and you accept a fussier print and, often, a hungrier nozzle to get it.

Fibre-filled: stiffer and more stable, but abrasive

Take a normal plastic — PLA, PETG, nylon — and blend in short carbon fibres (CF) or glass fibres (GF), and it changes character. The filled version is markedly stiffer and holds its dimensions better, because the fibres resist the shrinkage and creep that let the base plastic move. It also warps less and comes out with a handsome matte finish that hides layer lines. For jigs, structural brackets and parts that must stay flat and true, a filled filament is often the easiest way to get there.

Two costs come with the fibres. First, filled filaments are more brittle — the fibres stiffen the plastic but interrupt its ability to stretch, so a CF part is strong until it isn't, then it cracks rather than bends. Second, and this one bites hardware: the fibres are abrasive. They saw away at a standard brass nozzle from the inside, and within a spool or two the 0.4 mm hole is worn oversized and oval, quietly ruining every dimension after that.

Engineering plastics: nylon and PC

Some filaments are chosen for raw mechanical performance:

• Nylon (PA) is tough, slippery and wear-resistant — the go-to for printed gears, bushings, living hinges and any part that rubs against another. Its catch is moisture: nylon drinks water out of the air faster than almost anything, and prints badly wet, so it lives or dies by drying (Keeping filament dry). Filled nylon (PA-CF, PA-GF) tames its warping and stiffens it, and is one of the most useful functional materials there is.
• Polycarbonate (PC) is about impact and heat — extremely strong, hard to shatter, and stable at temperatures that soften everything else. It prints hot, warps like ABS, and is also hygroscopic. Reach for it when failure is not an option.

Aesthetic and support materials

The last group isn't about strength at all:

• Wood-, metal- and stone-filled filaments blend real particles into PLA for a look and feel — a matte wood grain you can sand, a metallic heft. Metal and stone are heavier; wood tends to weigh about the same or less. All are more brittle and mildly abrasive — metal fills and glow-in-the-dark blends do wear the nozzle, but milder than carbon or glass fibre, which are the heavy case — and still unbeatable for display pieces.
• Support materials print alongside your part and then vanish. PVA dissolves in water; HIPS dissolves in a solvent (and pairs with ABS). On a printer that can run two materials, they let you support complex overhangs and internal cavities cleanly, then wash the support away instead of prying it off — see Supports and bridging for when that's worth it.

Notice how many entries in that last column say the same two things — hardened nozzle and keep it dry. Those are the two hardware realities the specialty materials force on you. The second one is quiet, easy to ignore, and wrecks more prints than any other single cause: moisture. That's the last article in this section — Keeping filament dry.