In SLS, a laser selectively sinters the particles of a polymer powder, fusing them together and building a part layer-by-layer. The materials used in SLS are thermoplastic polymers that come in a granular form.

During the 3D printing process, the SLS machine preheats the bulk powder material in the powder bed somewhat below its melting point, to make it easier for the laser to raise the temperature of the selected regions the rest of the way to the melting point. A roller will apply a layer of polymer powder, then the laser will sinter the powder according to the 3D file and the build platform will lower before applying a new layer of powder. The process will be repeated until the desired part is created. 

SLS does not require support structures because unsintered powder surrounds the parts during printing. SLS printing can produce previously impossible complex geometries, such as interlocking or moving parts, parts with interior components or channels, and other highly complex designs.