Carbon fibre filament
Carbon fibre filament is a base plastic, such as nylon or PETG, mixed with short carbon fibres to make it stiffer and more stable.
Why it matters
The fibres change how the plastic behaves. Prusa says they improve dimensional stability and tensile strength, add heat resistance, and make the material lighter and less prone to warping. The trade-off is lower impact resistance and weaker layer adhesion.
The fibres are also highly abrasive. Prusa says you need a hardened steel nozzle, because a standard brass nozzle will wear down. Budget for that nozzle when you compare spool prices.
Settings follow the base plastic. Prusa gives a wide nozzle range of 240-285 °C and a bed range of 70-110 °C for these composites, depending on the filament. Check the spool label for your nozzle temperature.
Prusa also recommends at least a 0.4 mm nozzle and 0.2 mm layer height to lower clogging risk. Cheap composites are more likely to clog, ooze or snap in the printer.