Filaments are typically spooled strands of plastic materials, such as PLA (Polylactic Acid) or ABS (Acrylonitrile Butadiene Styrene). There are many other types available as well, including specialized materials like nylon, PETG, TPU (Thermoplastic Polyurethane), and more. Filaments are fed into the 3D printer where they are heated and extruded through a nozzle, allowing the printer to build up layers and create the desired object.