STL vs 3MF: STL stores a raw triangle mesh, while 3MF adds real-world units, colour, materials and print settings. When to use each, and how to convert them free.
STL and 3MF are both 3D-printing file formats, but STL stores only a raw triangle mesh of the surface, while 3MF is a newer format that bundles the mesh plus real-world units, color, materials, and print metadata in one file. STL is the long-standing universal format every slicer reads; 3MF is more modern, more compact, and less error-prone.
OwlCAD reads and writes both, with units detected on import, and everything works in true millimetres.
A raw triangle mesh of the model surface, unitless and universal. Every slicer, printer, and marketplace reads it, which makes it the safest choice when you don’t control the other end.
A modern container that bundles the mesh plus real-world units, color, materials, and print settings in one compact, less error-prone file. Better when a plain single-color mesh isn’t enough.
Open either format, edit or repair it, and export the other, plus OBJ and GLB, free and with no install.
Use STL for maximum compatibility: every slicer, printer and marketplace (Printables, MakerWorld, Thingiverse) accepts it. Use 3MF when you want to carry units, colour, or multi-material and print settings together, or want a smaller, more robust file. A 3MF saved by Bambu Studio or PrusaSlicer can also carry plates, colours and print settings (a project 3MF), while a plain 3MF holds the model with its units. For a plain single-colour print either works; for anything richer, prefer 3MF.
No. STL is unitless, which is why models sometimes import at the wrong size and need rescaling. 3MF records real-world units, so a part keeps its intended dimensions. OwlCAD works in true millimetres throughout and detects units on import, so models load at the right size either way.
Yes. OwlCAD imports either and exports the other, plus OBJ and GLB, free in your browser. Open an STL and export 3MF, or vice versa; you can also combine imported meshes with parametric shapes before exporting. A 3MF keeps its colours and object names on the way in, so a multi-material model survives the round trip instead of arriving as one grey lump.
3MF is the more modern, slicer-friendly choice (Bambu Studio, PrusaSlicer, Cura and OrcaSlicer all open it): smaller, unit-aware, and able to carry color and print settings. STL remains the safest universal option when you are unsure what the other end supports. OwlCAD reads and writes both, so you can pick per project.