A filament extruder is a machine used to create plastic filament for 3D printing. It works by melting plastic pellets and forcing the molten material through a nozzle to form a continuous strand. This filament can then be cooled and wound onto spools for later use in various 3D printers. These extruders can be used with different types of plastics, such as PLA or ABS, allowing users to customize their filament based on specific project needs. Filament extruders are popular among hobbyists and professionals alike, as they enable the production of high-quality, cost-effective filament at home.