Selective Laser Sintering (SLS) is a process that was patented in 1989 by Carl Deckard, a University of Texas graduate student. Its chief advantages over Stereo Lithography Apparatus (SLA) revolve around material properties. Many varying materials are possible and these materials can approximate the      properties of thermoplastics such as polycarbonate, nylon, or glass-filled nylon.
As the figure below shows, an SLS machine consists of two powder magazines on either side of the work area. The leveling roller moves powder over from one magazine, crossing over the work area to the other magazine. The laser then traces out the layer. The work platform moves down by the thickness of one layer and the roller then moves in the opposite direction. The process repeats until the part is complete.