STL file extension

File extension stl is probably best known for its use for 3D format used for 3D printers.

STL stands for Standard Tessellation Language, and as a format was developed by the Albert Consulting Group (Albert-Battaglin Consulting Group today) for 3D Systems in 1987 for moving 3D CAD models to its stereolithography apparatus (SLA) machines. Historically, the use of this format is tightly tied with stereolithography - 3D printing in series slices.

A, stl file describe only the surface geometry of a 3D object without any representation of color, texture or other common CAD model attributes. It exists in both binary and ASCII format and probably many variants were created through the years.

It is easy to output, so most CAD programs that deal with 3D models can export to STL.

Note that STL is one of the world's worst 3D file formats. Many people continue to believe it is a high quality CAD file format when that has little reality. It should never be used to convert data from one 3D program to another, and especially not from any CAD program. If you are sent a STL file then the data vendor should be asked for the original, native CAD file, IGES or STEP file instead.

A .stl file only contains a run of individual triangles with only vertex information and nothing else. There is no accurate vertex normals smoothing information, no uv texture coordinates or vertex colors, no materials, no hierarchy, no lights, no cameras, etc. It doesn't get much worse.

Note: In Windows, the STL extension is by default associated with Certificate Trust List. This is not in any way related to stereolithography.

MIME type:
application/sla

Updated: November 9, 2023