Carbon, Glass and Wood-Filled Filaments

What the fibers do

Prusa explains that carbon, glass or Kevlar fibers are mixed into a base polymer to improve its mechanical properties. Its list of gains: better dimensional stability, lighter parts, less warping, higher heat resistance and higher tensile yield strength. Its list of costs: usually lower impact resistance and weaker layer-to-layer adhesion, so the filament is more brittle. Uses Prusa names include RC drone frames, airframes, car parts and functional prototypes.

The base plastic still sets most of the behavior. Read the page for the base material too: PLA, PETG, Nylon.

"Carbon" does not always mean stiffer

Compare two Polymaker data sheets that use the same ISO test methods Maker spec:

Property	PolyLite PLA	PolyLite PLA-CF
Young's modulus (stiffness), along layers	about 3,430 MPa	about 3,280 MPa
Elongation at break, across layers	about 1.8 percent	about 0.9 percent
Nozzle range	190 to 230 °C	190 to 230 °C
Drying	55 °C for 6 hours	55 °C for 6 hours

In this pair the carbon version is not stiffer, and it stretches about half as far across layers before breaking, in line with Prusa's "more brittle". Polymaker describes PLA-CF as designed for functional applications and a smooth, matte surface finish. Some products add fiber for looks: Prusa notes its PETG Carbon Fiber black is filled with carbon for looks only. Judge a filled filament by its own data sheet, not by the word "carbon". Polymaker also states its data-sheet values are for reference and comparison, not design specifications.

Nozzles: abrasion and clogging

Prusa says a hardened nozzle is required because the fibers are highly abrasive. See Hardened Nozzles and Abrasive Filaments.

Fibers also raise the clogging risk. Prusa says a larger nozzle and taller layers lower it, and gives a 0.4 mm nozzle with 0.2 mm layers as the lowest optimal values Starting point. Prusa also recommends a cold pull to clean the nozzle before printing, warns that a poor first layer risks clogging the nozzle, and says cheap filled filaments often cause clogging, oozing and filament breakage. See Clogged Nozzle.

Temperatures, bed and enclosure

Prusa gives 240 to 285 °C at the nozzle and 70 to 110 °C at the bed for its carbon, Kevlar and glass fiber composites, depending on filament type Rule of thumb, and says they print slightly hotter than the unfilled version. That span covers several base plastics, so it is only a guide; the data sheet for your spool sets the range. Polymaker's PLA-CF, for example, lists the same nozzle range as its plain PLA. Bed preparation also depends on the filament type. Because fibers reduce warping, Prusa says its carbon-filled PA11 can print without the enclosure plain nylon benefits from.

Wood-filled filament

Wood filaments are a base plastic with wood particles mixed in. Prusa's Woodfill is a PLA-based filament filled with wood particles that give a natural color and matte finish, recommended for objects that should look like wood and do not need mechanical strength. Prusa lists it as brittle with poor high-temperature resistance.

Prusament Woodfill	Value
Nozzle	195 °C, plus or minus 10 Maker spec
Bed	60 °C, plus or minus 10 Maker spec
Nozzle size	Standard 0.4 mm brass works for this product Maker spec
Surface	Satin sheet, or smooth sheet with glue stick; not the textured sheet
Drying	Not needed before printing; Prusa's drying table gives 45 °C for 6 hours Maker spec

Prusa adds that most wood-powder filaments need a 0.6 mm or larger nozzle for best results Rule of thumb, so the 0.4 mm figure applies to Woodfill only. Woodfill grips PEI strongly, which is why Prusa calls for a separation layer on smooth sheets. Printed parts can be sanded and stained like real wood, which highlights the texture.

Ventilation and handling

Ventilate as you would for the base plastic; for polyamides, filled or not, see the warnings in Nylon (PA), where Prusa notes a strong odor and ultrafine particles. See FDM Emissions and Ventilation and the base material's page.

Moisture and storage

Dry and store a filled filament the way its maker says for that product. Prusa's drying table lists its filled materials separately, for example 90 °C for 6 hours for PA11 Carbon Fiber and 70 °C for 2 to 4 hours for its PP carbon and glass fiber grades Maker spec, and Prusa suggests a professional drying oven for carbon-filled nylons. See Drying and Storing Filament.

Common failures

What you see	Usual cause	Where to go
Nozzle clogs partway through	Small nozzle, poor first layer, low-quality filament	Clogged Nozzle
Extrusion slowly gets worse	Abrasive fill wearing a brass nozzle	Hardened Nozzles
Part snaps on impact	Some fills lower impact resistance (check the data sheet; not every filled grade does)	Compare impact figures on the data sheets, or use an unfilled grade
Filament breaks	Often low-quality filament, per Prusa	Try a different spool