You download a model to print and get .stl, .obj and .3mf files — or the print shop wants one format and you have another. Here's what each format holds and which one to pick.
In short
| Format | What it holds | Best for |
|---|---|---|
| STL | Shape as triangles; no colour or texture in the standard | 3D printing, used for decades |
| OBJ | Shape; colours and textures via a separate .mtl file | Exchanging models between programs |
| 3MF | Shape, units, colours, materials, several parts in one file | Modern 3D printing |
| glTF / GLB | Shape, colours, textures; units in metres | Showing models on the web |
- Everyday 3D printing: STL has been around longest and common slicers open it; 3MF holds more if your software and print shop support it.
- Want to keep colours or several parts: use 3MF.
- Showing a model on a website: use glTF or GLB.
STL: the original 3D-printing format
The US Library of Congress records that STL was first documented in 1988 by 3D Systems, for the stereolithography printers of the time.
STL stores the model's surface as triangles and nothing else; the standard has no support for colour or texture. It comes in text (ASCII) and binary versions, and binary is more common because it's smaller.
An STL holds only coordinates. If a model looks tiny or huge in your slicer, check the units and rescale it there.
OBJ: colours, but with a companion file
OBJ was first used by Wavefront Technologies around 1990. It's a text format treated as vendor-neutral. Colours and textures live in a separate .mtl file that has to travel with it.
Worth knowing for printing: Prusa says PrusaSlicer ignores material and texture information when importing OBJ — you get the shape only.
3MF: the modern 3D-printing format
3MF comes from the 3MF Consortium, announced together with the first specification in 2015, with Microsoft as the initiator. It is now also an international standard, ISO/IEC 25422:2025.
A 3MF is a ZIP containing XML. The core specification says a 3MF:
- can state the model's unit — millimetres if none is given;
- can hold several objects to build at once;
- can store colours and materials for each part.
Prusa explains that, unlike STL, a 3MF can store several models, slicer settings, a thumbnail, colour and texture — and is usually much smaller than STL. PrusaSlicer also uses 3MF for its project files.
One catch: Bambu Lab says Bambu Studio saves 3MF using the Production Extension by default, so some other slicers can't open 3MF files from Bambu Studio.
glTF and GLB: for the web, not for printing
glTF is an open standard from the Khronos Group, nicknamed "the JPEG of 3D", made for delivering and loading 3D models quickly in apps and on the web. The specification says all linear distances are in metres. GLB is glTF in a single file — great for showing models online, but most slicers don't use it as their main print format.
What slicers open
- PrusaSlicer: 3MF, STL, STEP, OBJ and AMF, with 3MF preferred.
- Bambu Studio: .3mf, .stl, .stp, .step, .amf and .obj.
Convert 3D files in your browser, without uploading
Convert 3D files opens 25 formats and saves 13, and you can turn the model around before downloading. Files are never uploaded.
- STL to 3MF and OBJ to 3MF: a 3MF in millimetres with each part's colour (no slicer settings).
- 3MF to STL: for software or shops that take STL only.
- OBJ to STL and GLB to STL: make web or game models ready to print.
- View 3D files: check the model, its size and triangle count before printing.
We never change a model's coordinates when converting. If the source used other units, check the scale in your slicer.
Note
This article is based on documents from the Library of Congress, the 3MF Consortium, Prusa, Bambu Lab and the Khronos Group, read on 28 September 2026. The formats each program supports can change between versions.
