FDM uses extrusion to lay down thin lines of thermoplastic material in the shape of the object being manufactured.

Only polymers with appropriate melting points and melt-flow characteristics can be used. Commercial FDM printers have commonly relied on materials such as ABS (acrylonitrile-butadiene-styrene) and PLA (polylactic acid), two common engineering plastics, as structural building materials.

One of the great benefits of this method is its simplicity. FDM constructs the model on a base plate that can move in the vertical direction. During manufacture, a filament of the feedstock polymer is fed into a heated melt chamber and heated to melting point. The heat-softened filament is extruded through a nozzle with a diameter of approximately 0.4 mm. The hot plastic is then laid down on the base plate, much like piping icing on a cake, by moving the extrusion head along a computer driven pathway over the build surface.

As the thermoplastic and the environment are hot, the material bonds with the build surface before cooling and hardening. Additional layers are built up in the same way, depositing more hot plastic on the layer previously put down, fusing the layers together and cooling to a solid state.

University of Wollongong, 3D Bioprinting: Printing parts for bodies, 2014, Wallace, G.G., Cornock, R.C., O’Connell, C.D., Beirne, S., Dodds, S., Gilbert, F.