STL vs 3MF: What's the Difference and Which Should You Use?
By 3DPrintMates Editorial · Published
STL stores only a surface made of triangles. 3MF stores the mesh plus units, colors, materials and (in slicer projects) print settings, in one compressed file. Use 3MF inside your own workflow and STL when sharing with tools or services that don’t accept 3MF.
What is an STL file?
STL dates back to 1987, when 3D Systems created it for the first stereolithography machines. An STL file is a list of triangles: each one has three corner points and a normal direction. That’s all. There are no units, no colors and no way to say which triangles belong to which part.
Because it is so simple, almost every CAD program, slicer and print service reads STL.
What is a 3MF file?
3MF (3D Manufacturing Format) was published in 2015 by the 3MF Consortium, an industry group that includes Microsoft and several 3D printer and software companies. A 3MF file is a ZIP archive containing XML that describes:
- one or more meshes with shared vertices,
- the unit (millimeter, inch, meter…),
- colors and materials,
- the build layout - and, in files saved by slicers like Bambu Studio or PrusaSlicer, plates and print settings.
STL vs 3MF compared
| STL | 3MF | |
|---|---|---|
| Units | None (assumed mm) | Declared in the file |
| Colors / materials | No | Yes |
| Multiple objects | Merged into one soup | Separate objects |
| Print settings | No | Slicer projects store them |
| File size | Large (vertices repeated) | Smaller (shared vertices + ZIP) |
| Support | Universal | All modern slicers, most CAD |
Why do STL files come in at the wrong size?
Because STL has no unit field, a file modeled in inches is read as millimeters and appears about 25× too small. 3MF avoids this by recording the unit. You can check any file’s real dimensions with the STL viewer.
Is 3MF better than STL?
For printing on your own machine, yes: you keep colors, settings and multiple parts in one file, and sizes are never ambiguous. STL is still the safer choice when you upload to model sites, send files to some print services or use older software.
How to convert between them
- 3MF to STL: extracts the geometry and merges all objects into one STL in millimeters.
- STL to 3MF: packages an STL with explicit millimeter units and deduplicated vertices.
Both converters run in your browser - the file is never uploaded.
Bottom line
Keep projects as 3MF. Export STL when someone else’s tool needs it.