Fused Deposition Modeling (FDM) works by extruding a thermoplastic material and depositing it layer-by-layer and fusing it to the layer beneath it, to form a 3D model.  A plastic filament is unwound from a coil and supplies material to an extrusion nozzle. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions.  The entire system is contained within a chamber which is held at a temperature just below the melting point of the plastic. FDM prototyping creates accurate, functional prototypes using high-performance engineering materials like ABS.  Many FDM techniques use two materials in the course of constructing parts. The first material is the part material and the second is the support material (to support overhanging features during construction). The support material is later removed by heat or dissolved away with a solvent or water.