SLA (Stereolithography)

SLA was invented by Chuck Hull in 1986, who founded 3D Systems to commercialize it. The original machines were large industrial systems aimed at engineering prototyping. Modern SLA — Formlabs is the best-known maker — uses a galvanometer-steered laser to draw each layer with sub-100-micron precision.

Because the laser writes the layer pixel by pixel, SLA is slower than mask-based methods (MSLA, DLP) but produces clean, isotropic parts with very fine surface detail. The process happens upside down in most desktop machines: the part hangs from the build platform and the laser fires upward through the bottom of the vat.

SLA is what you reach for when surface finish and detail beat everything else: jewelry casting masters, dental models, miniatures, hearing aids, prototypes that need to look like injection-molded parts. Layer lines are nearly invisible compared to FDM.

The cost is workflow overhead. Resin is messier and more toxic than filament. Parts need to be washed in isopropyl alcohol and post-cured under UV before they reach final strength. Supports are almost always required because parts hang from the build plate.

"SLA" in casual use often refers to all resin printing. Strictly, SLA uses a laser; MSLA uses an LCD mask; DLP uses a projector. For users, the print quality differences are smaller than the speed and cost differences.