View STL Format
The STL format is a mesh interchange format that was originally intended to send computer models to a 3D printer so that the computer model could be made into a physical object. This format is a triangles-only format. No higher level surface types are allowed, so whenever you save an object mesh into this format, make sure you understand what you are getting as a result of the translation. Most computer animation and modeling programs, as well as many CAD programs, support the STL format.
Note: in order to have a successful 3D printout from the STL format (or more correctly, meshes that are interchanged with the format), the model must be clean and well-built. It must be “watertight,” in that there are no “leaks” or errant holes within the mesh (make sure you weld your vertices). There should be no disconnected vertex, edge or face data, lest those elements cause the printing process to fail. There are several good, free utilities online that can check the validity of STL files, and their suitability for 3D printing.