Stereolithography (SLA) is an additive manufacturing process that builds objects by using an ultraviolet laser to selectively cure and harden liquid photopolymer resin one thin layer at a time.
Stereolithography is the oldest form of 📝3D Printing, patented by Chuck Hull in 1986; Hull went on to found 3D Systems and originated the widely used STL file format. It belongs to a category of processes called vat photopolymerization, which also includes digital light processing (DLP) and masked SLA (mSLA).
An SLA printer directs an ultraviolet laser across a vat of liquid photopolymer resin, tracing each cross-section of the model and curing the resin where the beam strikes it. Many desktop SLA printers work upside down, with a build platform that lifts out of the resin tank as each layer solidifies. The resulting layers can be thinner than a human hair, giving SLA its characteristic smooth surfaces and fine detail.
Printed parts emerge coated in uncured resin and require post-processing — typically washing in isopropyl alcohol followed by a final ultraviolet cure. Compared with filament-based extrusion, SLA achieves higher resolution but uses messier, light-sensitive materials, making it favored for dental, jewelry, and miniature applications.