Filaments for FDM 3D Printing (Fused Deposition Modeling, also known as Fused Filament Fabrication or FFF) are the thermoplastic materials used in the most popular and accessible form of 3D printing. These materials come in the form of thin, continuous strands (typically 1.75 mm or 2.85 mm in diameter) wound on spools. The filament is fed into a heated extruder nozzle, where it melts and is precisely deposited layer by layer onto a build platform to form solid objects.