The short answer
Use 3MF to share or archive a print project, especially with several parts or colours. Use STL when you need a file that absolutely every program accepts, or for a single-colour part you'll slice yourself.
| 3MF | STL | |
|---|---|---|
| Units | Stored (usually millimetres) | Not stored — assumed |
| Colours and materials | Yes | No |
| Several objects and parts | Yes, with names and positions | One mesh per file (in practice) |
| Print settings, plates | Yes, in slicer project files | No |
| File size | Compressed, shared vertices — small | Every triangle stores its 3 corners — large |
| Mesh errors | Spec requires closed, consistent meshes | Gaps and flipped faces are common |
| Compatibility | All current slicers; older tools vary | Everything |
Why 3MF files are smaller
An STL lists the three corners of every triangle, so a corner shared by six triangles is written six times, then left uncompressed. 3MF stores each corner once, references it by number and zips the result. The same model is typically several times smaller as 3MF.
The catch: slicer project 3MFs
When Bambu Studio, OrcaSlicer or PrusaSlicer save a project, they add their own settings and extensions to the 3MF. Another slicer may read the shapes but lose parts, colours or plates. Converting the project to a standard 3MF or to STL fixes that.
Converting
- 3MF to STL — whole project, a single plate, or one STL per object.
- STL to 3MF — combine several STLs into one 3MF.
Convert between 3MF and STL
Drop a 3MF file here
or drag it into this box · STL and OBJ work too
Your file is opened in this browser tab. Nothing is uploaded.
Frequently asked questions
Is 3MF better than STL?
For most 3D printing work, yes: it is smaller, stores units and colours, and keeps several objects together. STL is still the most compatible format.
Does converting STL to 3MF improve print quality?
No. The geometry is the same, so the print is the same. You gain smaller files, explicit units and the ability to keep several objects and colours in one file.
Can every slicer open 3MF?
Bambu Studio, OrcaSlicer, PrusaSlicer, Cura and most manufacturer slicers open standard 3MF. Project files with slicer-specific extensions open fully only in that slicer family.