4B Engraver3MF vs STL for personalised 3D prints
Print the 3MF when you want the part exactly as the designer set it up: the 3MF carries the print profile, the plate layout, the filament assignment and the paint-on supports along with the mesh. Use the STL when you are mixing several different parts on one plate, or when your slicer is not Bambu Studio. 4B Engraver writes both files for every part it engraves, so you can keep the decision until you are actually at the slicer.
The difference bites hardest on parts designed with painted supports. An STL discards that data silently, and the print then fails in a way that looks like a slicer problem rather than a file problem.
What does a 3MF carry that an STL does not?
An STL is a list of triangles and nothing else. No settings, no colours, no supports. It is old, readable by everything, and completely silent about how the part should be printed.
A 3MF saved as a Bambu Studio project is a zipped container. Alongside the mesh it stores the print profile (layer height, wall count, infill, support settings), where the object sits on the plate, which filament each object uses, the preview thumbnails, and per-triangle painted data. That last item includes paint_supports: the paint-on supports someone brushed onto specific faces by hand.
| What it carries | 3MF (Bambu Studio project) | STL |
|---|---|---|
| Mesh geometry | Yes | Yes |
| Print profile (layer height, walls, infill, supports) | Yes | No |
| Plate layout | Yes | No |
| Filament assignment | Yes | No |
Painted supports (paint_supports, per triangle) | Yes | No |
| Colours | Yes | No |
| Thumbnails | Yes | No |
What happens when painted supports get dropped?
We hit this for real. An early build of the engraver rewrote the 3MF after cutting the text and, in doing so, lost the painted-support data. Geometry was fine. The part sliced without complaint. The print came off the plate with a rough, sagging ceiling inside the connector pocket, because the bridge over that pocket had been printed unsupported: its paint-on supports no longer existed in the file.
That is not a small amount of data to lose. The two bundled Apple cable winders carry 2,494 painted-support triangles (1 m USB-C-to-USB-C) and 2,812 (MagSafe spooler). Engraving destroys and rebuilds triangles in the cut area, so the engraver now transfers the painted data onto the surviving triangles by matching triangle centroids, and the brushwork comes through to the output 3MF intact.
How big are the files?
3MF is a compressed container, so for the same mesh it is the smaller file. These are measured outputs from the tool:
| Model | 3MF | STL | Painted-support triangles |
|---|---|---|---|
| 1 m USB-C-to-USB-C winder | 7.9 MB | 27.6 MB | 2,494 |
| MagSafe spooler (1.99 M triangles) | 26.8 MB | about 60 MB | 2,812 |
Both measured pairs put the 3MF between a quarter and a half the size of the STL, so it uploads faster as well. The engraver accepts files up to 80 MB, and it is the dense STL that gets anywhere near that: the MagSafe spooler is about 60 MB as an STL against 26.8 MB as a 3MF.
When is STL genuinely the better choice?
- Mixing several different parts on one plate. You want your own layout and your own profile, not four designers' conflicting ones. Import the geometry, arrange it, slice it your way.
- Any slicer that is not Bambu Studio. The profile and the painted supports in a Bambu project file are written for Bambu Studio, so elsewhere the geometry is the part worth carrying across and you will be setting the print up yourself anyway.
- Handing geometry to someone else when you have no idea what printer or software is at the other end.
When should you stick with the 3MF?
- The part has painted supports, painted colours, or a profile the designer clearly tuned.
- You are printing a two-colour engraving. Pausing for a filament swap at the layer where the recess floor sits fills the letters with a second colour, and that depends on knowing the layer height the profile sets. The default 1.2 mm depth is exactly 10 layers at 0.12 mm; see how deep to engrave.
- You are reprinting a personalised part months later and want it to come out identical.
Which format does the engraver give you?
Both, every time, for every part. Upload a single-object STL or 3MF, or start from one of the two built-in winders, add a name, a serial or your own logo, and the download contains a 3MF and an STL of the same engraved model. Generation takes roughly 3 to 10 seconds per part. Every output is checked watertight, and each engraved floor is verified to exist at the depth you asked for. Batch runs with consecutive serials arrive as one zip with both formats per part, so a plate of twenty numbered units is still a single decision at the slicer, not twenty.
Try it on your own model. Upload an STL or 3MF, add a logo, a name or a serial number, and download a print-ready file.
Open the engraver — freeFrequently asked questions
Does exporting a 3MF to STL lose the supports?
Yes. Paint-on supports are stored as per-triangle data inside the 3MF, and an STL has nowhere to put them. The export succeeds, the mesh is identical, and the supports simply cease to exist. We saw exactly that failure when an early build of the engraver dropped the painted data while rewriting a 3MF: the ceiling inside the connector pocket came out rough and sagging over the unsupported bridge.
Is a 3MF always smaller than an STL of the same part?
In practice yes, because 3MF is a zipped container while STL stores triangles uncompressed. Measured on our two winders: the 1 m USB-C-to-USB-C model is 7.9 MB as 3MF against 27.6 MB as STL, and the MagSafe spooler at 1.99 million triangles is 26.8 MB against roughly 60 MB.
Which file should I hand to someone else to print?
Send the 3MF if they run Bambu Studio and you want the profile, plate layout, filament assignment and painted supports to survive. Send the STL if you do not know their setup, or if they will be arranging your part alongside other models on their own plate with their own settings. Sending both costs nothing.
Does engraving text into a model damage its painted supports?
It changes the triangles in the cut area, so naive rewriting does lose them. The engraver handles this by matching triangle centroids and transferring the painted data onto the triangles that survive the cut, so the output 3MF keeps the original paint-on supports: 2,494 triangles on the 1 m winder, 2,812 on the MagSafe spooler.
I want to print six different personalised parts on one plate. Which format?
Use the STL files. Six 3MF project files bring six sets of print settings and six plate layouts, which conflict as soon as you combine them. Import the STLs into one project, arrange them yourself and apply a single profile. The one exception is a part that needs painted supports, which is worth printing on its own plate from its 3MF.