.stl File — Stereolithography / 3D Printing Model

STL (Stereolithography) is a file format native to the stereolithography CAD software created by 3D Systems, and has become the de facto standard for 3D printing. STL files describe the surface geometry of a 3D object using a mesh of triangular facets, each defined by three vertices and a normal vector indicating the outward direction. The format comes in two variants: ASCII (human-readable text) and binary (more compact, typically 50x smaller). STL files represent only surface geometry without color, texture, material properties, or internal structure — the model must be a closed, watertight solid manifold for proper 3D printing. Despite its limitations, STL's simplicity and universal support in 3D printing software (slicers like Cura, PrusaSlicer, and Simplify3D) have kept it as the primary file format for additive manufacturing. The format is used across industries including aerospace, automotive, medical (prosthetics, dental), architecture, consumer products, and hobbyist 3D printing. Newer formats like 3MF (3D Manufacturing Format) address STL's limitations by supporting colors, materials, and metadata, but STL remains the most widely supported format in the 3D printing ecosystem.