Stereolithography .stl
Naked triangles for 3D printing. No colour, no UVs, no hierarchy.
What an .stl file holds
STL describes a solid as an unstructured soup of triangles, each with a normal and three corners, and nothing else. No colour, no texture coordinates, no units, no scene graph, which is exactly why every slicer and every 3D printer on the market accepts it. Converting to STL flattens your scene into a single watertight-ish mesh and throws the materials away; that loss is intentional, not a bug.
Commonly seen in: Cura, PrusaSlicer, Bambu Studio, Fusion 360, SolidWorks, Meshmixer.
| Data | Stored in STL |
|---|---|
| Geometry | Yes |
| Materials and colour | No |
| Texture maps | No |
| Animation and rigs | No |
| Scene hierarchy | No |
| Read here | Yes |
| Written here | Yes |
Tested against a real file
The last sweep loaded sphereWithHole.stl from Assimp test models through the viewer on this site: 285 triangles across 1 meshes and 1 materials, in 1.8 seconds. Every format's result is on the test results page, run 2026-09-08.
Convert STL to another format
Every pairing has a page saying what survives the trip.
Convert something else to STL
Other things to do with an .stl file
Questions about STL
How do I open an .stl file?
Drop it into the viewer on this site and it opens in the browser, with the scene tree, the materials and the mesh statistics. Nothing is uploaded. If you want it in another program instead, convert it to GLB, which almost everything reads.
Is STL a good format to archive in?
STL stores geometry. Anything outside that list will not be in the file at all, so archive the original alongside it if the surfacing or the rig matters.
Does converting STL lose quality?
Geometry is copied vertex for vertex, so the shape does not degrade. What gets lost is whatever the target format has no field for: convert to STL and the materials go, convert to OBJ and the animation goes. The comparison table on each converter page says exactly which.
Written up on the blog
Formats that hold the same things
Or go back to the full format reference.