STL vs 3MF: Which 3D Printing File Format Should You Use?
STL is the classic 3D printing format, but 3MF carries units, colour and multi-part data. How they differ, how to export each, and which to send us.
When you export a model for 3D printing, you usually choose between two formats: STL and 3MF. STL has been the default for decades, but 3MF is a modern replacement that carries far more information. Here is how they differ, what that means for your quote, and which one to send for the best results.
What STL Actually Stores
An STL file describes only the surface of your model as a mesh of triangles. That is it — no units, no colour, no materials, no print settings. It is simple and universally supported, which is why it became the standard three decades ago. But that simplicity is also its weakness: a lot of useful information is thrown away on export, and has to be re-specified by hand every time.
What 3MF Adds
3MF (3D Manufacturing Format) is a newer, XML-based, zip-packaged format designed specifically for modern 3D printing. Alongside the geometry it can carry:
- Units and scale — so there is no ambiguity about whether your part is in millimetres or inches.
- Colours and materials — useful for multi-colour and multi-material prints, including which part is assigned to which filament slot.
- Multiple objects — several parts and their arrangement on the build plate in one file.
- Print settings — orientation, supports and slicer configuration can travel with the model.
- Better integrity — the format is less prone to the gaps and non-manifold errors that plague STL meshes.
Side-by-Side
| Factor | STL | 3MF |
|---|---|---|
| Geometry | Triangle mesh only | Triangle mesh |
| Units / scale | None (ambiguous) | Defined |
| Colour / material | No | Yes |
| Multiple parts | One per file | Many per file |
| Print settings | No | Optional |
| File size | Larger for fine detail | Usually smaller (compressed) |
| Support | Universal | Very wide and growing |
The Scale Problem STL Causes
Because STL stores no units, a model exported in inches can arrive looking 25.4 times too small (or too large) when opened as millimetres. A part meant to be 50 mm across imports as 1,270 mm if the units were misread the other way — instantly turning a keychain into something the size of a car. This is one of the most common causes of confusion in quoting and printing, and it is entirely avoidable. 3MF eliminates the guesswork by recording the units explicitly, so the file always imports at the size you designed.
Multi-Colour Files and Our Printers
This is where 3MF earns its keep for us specifically. We run the Bambu Lab H2 series in-house: the H2D with dual independent nozzles, and the H2C with an eight-hotend swap system supporting up to seven colours in a single print. If you send us a project-format 3MF exported from a slicer like Bambu Studio — rather than a plain single-body export straight from CAD — it can carry the per-part filament assignment baked in. Our system reads which parts are assigned to which colour slot and prices the job accordingly, including the extra time and material waste that swapping filament mid-print adds. An STL has no concept of "this part is red, this part is black" — you would need to describe that separately in a message, and there is more room for a mix-up.
A plain 3MF exported straight from CAD software (Fusion 360, SolidWorks and so on) does not carry this Bambu-specific colour data on its own — that comes from a slicer project export, not the CAD export itself. Either way, geometry, units and single-colour parts work identically in both formats; this only matters once colour-per-part enters the picture.
Exporting 3MF from Common Tools
- Fusion 360 — "Export" then choose 3MF from the format dropdown; units and colour styles carry over automatically.
- SolidWorks — "Save As" and select 3MF; assembly colours are preserved per part.
- OnShape — export a Part Studio or Assembly as 3MF from the export dialog.
- Bambu Studio / PrusaSlicer / Cura — "Save Project As" 3MF captures the full plate, including per-object filament assignment, orientation and any supports you've already configured.
- Blender — the 3MF import/export add-on (bundled with recent versions, otherwise installable from Preferences) handles it; export scale defaults to metres, so double-check the unit setting before sending.
If your software does not offer 3MF at all, a correctly scaled, binary STL is still a completely safe choice — see our guide to preparing STL files for printing for export settings that avoid the usual mistakes.
Which Should You Use?
If your CAD or modelling software can export 3MF, prefer it — especially for parts where scale, colour or multiple components matter. It carries more information, is generally more reliable, and avoids unit mix-ups. Regardless of material — from our most affordable PLA up to structural PA-CF — the quote tool reads grams and geometry the same way once the file is uploaded, so format choice never changes what you pay; it only changes how much has to be double-checked by hand.
STL is still perfectly fine for simple, single-colour parts, and remains the most universally compatible option. If 3MF is not available, a correctly scaled STL exported at a sensible resolution will print just as well.
A Quick Export Tip
Whichever format you choose, export at a resolution that keeps curves smooth without ballooning the file size — extremely high-resolution meshes rarely improve the printed result and just make files harder to handle. Our upload limit is 100 MB either way, and a well-prepared file of either format is usually well under 10 MB.
Have a file ready? Upload your STL or 3MF for an instant quote — and if anything looks off with the scale, we will flag it before printing.
We accept both formats — upload your file and get an instant price, no matter which one you send.
