FDM, also known as FFF (fused filament fabrication), is a 3D printing method where materials (thermoplastic filaments) are extruded through a nozzle onto a tray to build a part layer by layer from a bottom up. With FDM printing, a wide variety of materials can be printed with relatively few modifications, meaning that a single FDM 3D printer can produce parts with different properties and appearances just by changing the type of filament.