How to open a 3MF file online
A 3MF is one package, so a single file is all that is needed. Drop it on the panel above, or press Open 3D file(s).
Open the package
The model part is read from the archive and the scene is framed to fit. A package that is not a valid zip is reported as an archive error instead of an empty view.
Check components and the unit
Overview lists meshes, triangles, vertices and the bounding box, with the unit declared by the model part beside the dimensions.
Look from a few angles, then save
Top, Front and Right give known directions. Export PNG saves the current view for a note or a message.
What is inside a 3MF file
A 3MF is a zip package, not a single mesh. One part holds the model as XML: a build list, objects made of components and meshes, and optional material and colour groups. Other parts describe content types and relationships, and a package may also carry thumbnails or slicer settings. The viewer reads the model part and the unit it declares.
Because it is a package, a damaged 3MF usually fails at the container level. The viewer reports that the archive could not be read, which is a different problem from a mesh that is broken inside a readable package.
Components, colour and the declared unit
Objects and components become meshes, named from the model XML where the file provides names. The unit attribute on <model> is shown in Overview next to the dimensions: millimetre, inch, micron and the other values the format defines. When the attribute is absent, the size is reported as source units.
The Materials panel reports what the package's material and colour groups produce; a package without them shows a neutral surface and says so rather than inventing a colour.
3MF vs STL: six differences
Both formats describe a printable object, and they disagree on almost everything around the triangles.
| 3MF | STL | |
|---|---|---|
| Unit | declared in the model part | none |
| Material | base materials in the package | none |
| Colour | colour groups | none |
| Components | object and component tree | flat triangle list |
| Print settings | can live in the package; not applied here | none |
| Container | zip package | one binary or text file |
The STL viewer opens the geometry-only case, which is still what most printers accept directly. A 3MF is the better carrier when the unit, the components or the colours have to survive the trip.
What the viewer does not check
Printability
Wall thickness, overhangs, supports and bridging are slicer work. The panels describe the file, and nothing here predicts a print.
Slicer settings inside the package
A 3MF can carry print settings as separate parts. They are not read or applied, so the model is shown as geometry with its own materials.
Unit conversion
The declared unit is reported, not converted. A part declared in inches keeps its inch numbers.
Limits and questions
Does it show colours?
The Materials panel reports what the package's material and colour groups produce. A package without them is shown with a neutral surface.
Can a 3MF be edited or converted?
No. The viewer opens, inspects and exports a PNG; it does not write a model file back.
Why does the unit say source units?
The model part did not declare one. The numbers are unchanged, and no millimetre value is assumed.
What about a corrupt package?
The archive error is reported as a sentence and the page stays usable. A package that opens but contains no mesh is reported as an empty scene.
Are files uploaded?
No. The package is read in the browser and never sent anywhere.