What it stores
- Triangle geometry, in binary or ASCII
- Per-facet normals, often ignored by tools
- Several shells in the same file
3D FILE FORMAT
STL: the triangle-only format
STL is the lowest common denominator of 3D printing: a list of triangles with no unit, no colour and no material. It is still the safest file to hand to a slicer.
At a glance
What it does not store
- Units: the numbers are unitless
- Colours, materials and textures
- Shared topology: vertices are duplicated
- Objects, parts and metadata
When to use it
- Sending a mesh to a slicer
- Exchanging a simple surface between tools
- A quick visual check
Limits to know
- Slicers usually assume millimetres
- A non-watertight STL slices badly
- ASCII STL is 3–6× larger than binary
Convert to and from
STL → OBJConvert STL to OBJSTL → GLBConvert STL to GLBSTL → 3MFConvert STL to 3MFSTL → PLYConvert STL to PLYSTL → STLCompress an STL fileOBJ → STLConvert OBJ to STLGLB → STLConvert GLB to STLPLY → STLConvert PLY to STL3MF → STLConvert 3MF to STL
Questions about the format
Is an STL always watertight?+
No. STL only stores triangles; holes, flipped normals and separate shells are kept as-is.
Does STL store units?+
No. 1.0 is just a number; most slicers interpret it as millimetres.
ASCII or binary STL?+
Binary. It is 3 to 6 times smaller and loads faster in every slicer.