What a 3MF file actually is
A 3MF file is a ZIP archive. Inside it are XML "model parts" that hold the triangle meshes, plus relationship files that say which part is the main one, and optional extras such as thumbnails, textures and slicer settings. The format is maintained by the 3MF Consortium, and unlike STL it records the unit of measurement, colour and material assignments, and how several objects are placed relative to each other.
That richness is why "it opens in my slicer but not in this viewer" is a common complaint. Many general 3D viewers read only the simplest layout: one model part with all the meshes in it. Real-world printing files often look different.
Why Bambu Studio and OrcaSlicer files break other viewers
Bambu Studio and OrcaSlicer save projects using the 3MF Production
extension. Each object's mesh lives in its own file under 3D/Objects/, and
the main model part refers to those files through components with a p:path
attribute. Every one of those object files declares its own object with id
1, so a reader that keys objects by id across the whole archive mixes them
up — or finds nothing at all.
Mes3D follows the package the way the specification intends:
- it finds the root model part from the package relationships (falling back to
3D/3dmodel.model); - object and material ids are scoped to the file that declares them;
- components and build items are followed across files through
p:path, with their transforms applied; - the model's declared unit is converted to millimetres;
- when there is no usable build section, the top-level objects are shown instead of an empty scene.
The result is that a multi-part project opens with every part where the slicer had it.
Colours
Colours are read from the 3MF's standard base materials and colour groups and applied per triangle, falling back to the object's default colour. Switch the model colour to Original in the toolbar to see them; any other colour choice overrides them so you can inspect the shape on its own.
One caveat for multi-colour printing: Bambu Studio and OrcaSlicer store the regions you paint for the AMS, and which filament each object uses, in their own project data rather than as 3MF colour groups. Those choices are not shown — the geometry is, so you can still check every part before printing.
"This 3MF only contains G-code"
When you export a sliced plate from Bambu Studio or OrcaSlicer, the 3MF
you get (often named .gcode.3mf) is a print job. It holds the toolpaths as
Metadata/plate_N.gcode, and frequently not the geometry you modelled. A viewer
that does not check for this simply shows nothing.
Mes3D detects this case and says so. The fix is to open the project file you saved from the slicer (File → Save Project), not the exported print file.
How to open a 3MF file here
- Drag the
.3mffile onto the drop zone above, or click Choose 3D file. - The model opens full screen. Drag to rotate, scroll or pinch to zoom, and right-drag or two-finger drag to pan.
- Use the preset views (front, top, side…) and switch between perspective and orthographic projection to check alignment.
- On a computer, click two points to measure the distance between them in millimetres, or open the analysis panel for volume, surface area, estimated print weight, watertightness and overhang ratio.
Everything runs in your browser. The file is read from your disk into memory and never sent to a server, which matters when the model is client work or an unreleased product.
3MF compared with STL for printing
| 3MF | STL | |
|---|---|---|
| Units | Stored in the file | Not stored — the receiver guesses |
| Colour and materials | Yes | No |
| Several objects with placement | Yes | One undivided triangle list |
| Slicer settings | Optional, in the package | No |
| File size | Compressed ZIP | Uncompressed, ~50 bytes per triangle (binary) |
| Support | Modern slicers and CAD | Everything |
If you are sending a model to someone with a modern slicer, 3MF loses less information. If you do not know what they use, STL is still the safe fallback.
On a phone
In a mobile browser the viewer handles opening, rotating, zooming and the
dimensions panel. The Mes3D app for iPhone, iPad and Android opens 3MF files
from Files, Mail or a download with one tap, and adds measuring, mesh analysis
and cross-sections, plus exporting a resized or cut model back to 3MF with
its colours. On iPhone and iPad it also lets you place the model in AR, and
once it is installed, .3mf files show a 3D preview and thumbnail right in the
Files app.
Limits
- Files up to 200 MB open in the browser; very large multi-plate projects can take a few seconds to assemble.
- Textures stored in a 3MF are not displayed; per-triangle colours are.
- Slicer-only data such as supports, seams and modifier volumes is not drawn — this is a model viewer, not a slicer preview.