Filaments used in 3D printing are thermoplastics, which are plastics (aka polymers) that melt rather than burn when heated. These can be shaped and moulded, and solidify when cooled. The filament is fed into a heating chamber in the printer’s extruder assembly, where it is heated to its melting point and then extruded (squirted) through a metal nozzle as the extruder assembly moves. This traces a path programmed into a 3D object file to create, layer by layer, the printed object.