What's Wrong With STL?
Nothing is "wrong" with STL exactly — it works. But it was designed for a world that no longer exists, and its limitations create real problems in modern 3D printing workflows.
No unit information
STL files have no concept of units. A value of "50" in an STL file could mean 50mm, 50 inches, or 50 feet. Every slicer has to guess — and they don't always agree. This is why you sometimes import an STL and your model is 25.4× too large or too small. That factor of 25.4 is the mm/inch conversion ratio. 3MF embeds units explicitly.
No scale or orientation metadata
STL carries no information about how the model should be oriented, what scale it was designed at, or what material it's intended for. Every time you open an STL in a slicer, you start from scratch. 3MF can embed all of this.
No colour or multi-material support
STL is a single-material format. There's no standard way to define which parts of a model should be printed in which material or colour. 3MF supports multi-material definitions natively — essential for AMS users on Bambu Lab printers.
Binary vs ASCII fragmentation
STL comes in two incompatible variants: ASCII and binary. Software has to detect which format it's reading. 3MF is always XML-based and always structured the same way.
What 3MF Gets Right
3MF was developed by the 3MF Consortium — a group that includes Microsoft, Autodesk, Ultimaker, and HP — specifically to replace STL for modern 3D printing. It's a ZIP archive containing XML geometry data, plus metadata, materials, and print settings.
| Feature | STL | 3MF |
|---|---|---|
| Units embedded | ✗ None | ✓ Always mm |
| Scale metadata | ✗ None | ✓ Supported |
| Multi-material | ✗ Not supported | ✓ Native support |
| Colour information | ✗ Not supported | ✓ Per-face colours |
| File size | Medium | ✓ Smaller (compressed) |
| Slicer support | ✓ Universal | ⚠ Modern slicers only |
| Standard age | 1987 | 2015 |
3MF on Bambu Lab Printers
If you own a Bambu Lab X1C, P1S, A1, or any Bambu printer with AMS, 3MF is not just better — it's essential for multi-colour workflows. Bambu Studio's native project format is 3MF. When you save a Bambu Studio project, it saves as a 3MF file containing your model, your print settings, your filament assignments, and your support structures.
✓ Bambu best practice: If you're importing a model to print on a Bambu printer, import as 3MF whenever possible. If you only have STL, convert to 3MF first using Simpel3D — the file will import with correct units and no scale surprises.
3MF on PrusaSlicer and Cura
PrusaSlicer has supported 3MF since version 2.0 (2019). It's the recommended format for saving PrusaSlicer projects. Cura has supported 3MF since version 4.0. Both slicers treat 3MF as a first-class format and often have better import behaviour than STL — particularly around units and orientation.
How to Convert STEP, STL, or OBJ to 3MF
Any file in Simpel3D can be converted to 3MF. Drop your STEP, STL, or OBJ file onto the drop zone, select "3MF" as the output format, and download. The output is a valid 3MF file with correct structure — tested in Cura, PrusaSlicer, and Bambu Studio.
The conversion happens entirely in your browser via WebAssembly. Your original file never leaves your machine.
STEP → 3MF
The best path for CAD-originated models. STEP preserves exact geometry which tessellates cleanly to 3MF mesh. Perfect for Fusion 360, SolidWorks, and FreeCAD exports.
STL → 3MF
Useful when you have existing STL files that your slicer is mishandling due to unit confusion. Converting to 3MF embeds the correct unit context.
OBJ → 3MF
Common for Blender and photogrammetry outputs. OBJ files often have correct geometry but awkward scale — converting to 3MF and opening in a slicer tends to behave more predictably.
💡 What about converting 3MF back to STEP? This isn't possible — not because of a software limitation, but because converting a mesh back to parametric CAD is reverse engineering, not conversion. No tool does this reliably. STEP is always the starting format.
Should You Always Use 3MF?
Not necessarily. STL remains the right choice when:
- You're using an older slicer that doesn't support 3MF well
- You're sharing files with someone whose workflow is STL-based
- You're uploading to a 3D printing service that requires STL
- You're using software that only reads STL
In all other cases — especially on Bambu Lab, PrusaSlicer, and modern Cura — 3MF is the better choice. Less friction, fewer surprises, smaller files.
Convert to 3MF right now — free
STEP, STL, OBJ, IGES → 3MF. No upload, no account, no surprises.
Open Simpel3D Free →5 free conversions/day · Works in Chrome, Firefox, Edge