SLS (Selective Laser Sintering)

SLS was developed at the University of Texas at Austin in the mid-1980s. A heated build chamber holds a bed of polymer powder — usually nylon (PA12 or PA11). For each layer, a laser scans across the surface and sinters the powder where the part should be. A roller deposits a fresh layer of powder on top, and the process repeats.

When the print finishes, the part is buried in a cake of fused and unfused powder. You break it out, blast off loose powder, and the part is done — strong, isotropic, and ready to use.

SLS is the right choice for functional production parts in plastic. The unsintered powder supports overhangs naturally, so designs do not need printed supports — you can print a part with internal channels, lattices, or interlocking moving assemblies in one go.

Mechanically, SLS nylon is the closest plastic 3D printing comes to injection-molded strength. The catch is access — desktop SLS (Formlabs Fuse, Sintratec) exists but is expensive, so most users go through a service bureau.

SLS prints have a slightly grainy surface — the unsintered powder texture transfers to the part. For glossy or smooth finishes, you vapor-polish, dye, or media-blast.

SLS and MJF (HP's Multi Jet Fusion) target the same use cases and produce comparable parts. MJF uses a different fusing mechanism — a printed binder agent plus IR light — and tends to be slightly faster.