File formats
STL
Definition
STL is a simple mesh file format that stores a surface as a list of triangles, each with a normal and three vertices. It is the long-standing default for 3D printing, but it has no units, colors, or exact geometry.
Also known as: stereolithography file, .stl, StL
Updated
What is in the file#
According to the fabbers.com summary of the 3D Systems specification, an STL file is a list of facets, and each facet has a unit normal and three vertices. Files come in ASCII and binary versions. The format carries no scale information, so the coordinates are in arbitrary units and the slicer or CAD program has to assume millimeters or inches.
When to use it#
STL is fine for sending a finished part to a printer or slicer. It is a poor format for design exchange because the exact geometry is gone. For editing, send STEP. For printing with units, colors, or multiple parts, 3MF carries more information.
Sources
Related terms
Mesh
A mesh represents a shape as a surface of small flat polygons, almost always triangles, joined at shared edges and vertices. Meshes work well for rendering, games, and 3D printing, but they have no true faces, edges, or exact curves, so they are hard to dimension or edit as engineering geometry.
3MF
3MF is an XML-based file format for additive manufacturing maintained by the 3MF Consortium. Unlike STL it can carry units, colors, materials, and multiple objects in one package, but its geometry is still a triangle mesh, not editable CAD geometry.
Manifold
A manifold mesh is one where every edge is shared by exactly two triangles, so the surface clearly separates inside from outside. Slicers, mesh booleans, and CAD imports rely on manifold geometry to behave predictably.
STEP
STEP is the ISO 10303 family of standards for exchanging 3D product data between CAD systems, usually saved as .step or .stp files. A STEP file carries exact B-Rep solid geometry that another CAD program can measure and edit, but it normally does not carry the original feature history.