How to open, inspect and edit 3MF files (Bambu, Prusa, Orca projects)

A 3MF file is a ZIP archive with an XML mesh inside, so you can open it in any slicer, unzip it to see what is there, or pull the plain STL out in a few seconds.

Updated 27 October 2026 · 7 min read

What a 3MF file is

3MF (3D Manufacturing Format) is a ZIP package, not a single mesh file like STL. Rename part.3mf to part.zip and open it: you will see a fixed folder layout.

• [Content_Types].xml and _rels/.rels: package plumbing, borrowed from the Office Open XML format.
• 3D/3dmodel.model: the mesh itself. An XML file with a <vertices> list, a <triangles> list that indexes into it, one or more <object> elements and a <build> section with the transform of each placed item. The root element declares the unit (millimetre by default).
• Metadata/: thumbnails (thumbnail.png, usually 256 or 512 px) and application data.
• Optional 3D/Textures/ for colour textures.

That is the core specification. Slicers add their own files on top, which is why a project from one slicer does not fully open in another.

What each slicer stores inside

The practical consequence: a Bambu project opened in PrusaSlicer gives you the meshes, names and positions, but not the filament profile or paint-on supports. The mesh part is always portable; the settings are not.

Opening a 3MF: the options

Any slicer

Drag the file onto Bambu Studio, Orca Slicer, PrusaSlicer, SuperSlicer, Cura, Chitubox or Lychee. All of them read the core mesh. Bambu Studio and PrusaSlicer will ask whether to open it as a project (loading settings) or import geometry only. Choose Import geometry when you just want the parts; choose the project option when it came from the same slicer and you want the profile too.

In PrusaSlicer the prompt reads "Load config?" with options for printer, filament and print profile. In Bambu Studio, File > Import > Import 3MF/STL/STEP imports geometry only, while File > Open Project loads everything.

Windows 10 and 11

3D Viewer (preinstalled on Windows 10, available from the Microsoft Store on 11) opens 3MF directly with a double-click, shows colours and lets you rotate and measure. Paint 3D also opens it. Neither shows slicer settings.

macOS

Finder's Quick Look does not preview 3MF. Use a slicer, or Blender 4.x with the 3MF add-on (community add-on, enable under Edit > Preferences > Add-ons). Fusion 360 and Shapr3D import 3MF as a mesh body.

Browser

The 3MF viewer opens the package in the browser, applies the build transforms so multi-part plates show correctly, lists each object by name and reports dimensions and triangle count. Nothing is uploaded; the ZIP is unpacked and parsed locally.

CAD programs

Fusion 360: File > Open or Insert > Insert Mesh. SolidWorks 2019 and later: File > Open with file type set to 3MF, imports as a mesh body or graphics body. FreeCAD: File > Import via the Mesh workbench. In all cases you get a mesh, not editable solid geometry.

Getting the STL out of a 3MF

Three ways, depending on what you have installed.

From a slicer

PrusaSlicer: select the object, File > Export > Export Plate as STL for everything, or right-click the object and choose Export as STL/OBJ for one part. Bambu Studio: right-click the object, Export as one STL or Export as STLs (one file per part). Cura: File > Export, pick STL, which merges the whole plate.

Directly in the browser

The 3MF to STL converter reads the package, applies each build item's position and rotation, and writes binary STL. You can export all objects merged or each object as its own STL. For a folder of project files, the batch converter processes them in one go.

By hand

Unzip the file and open 3D/3dmodel.model. The XML is readable, but it is not STL, so you still need a converter. This route is mainly useful to confirm what is inside or to recover a mesh from a corrupted package where the ZIP central directory is damaged (7-Zip can often extract individual files even then).

When extracting from Bambu Studio projects, note that the meshes may be in 3D/Objects/object_1.model and similar, referenced from the main model file by path. A converter that only reads 3dmodel.model and ignores these references will produce an empty STL. Check the result in the STL viewer and compare the triangle count against what the slicer reports.

Editing a 3MF

Changing settings and layout

Do this in the slicer that made the file. Open the project, change what you need, File > Save Project. The mesh is untouched; only the configuration files inside the ZIP are rewritten.

Changing the mesh

A 3MF is not a CAD file. To change geometry you need either the original CAD model or a mesh editor. Blender (with the 3MF add-on), Meshmixer (discontinued but still available) and MeshLab all work on the triangles. For simple operations, cutting a large part into pieces or scaling to fit a different printer, the STL splitter and scale tool handle it on the extracted STL, after which you can save a new 3MF with the STL to 3MF converter or just import the STL into your slicer.

Removing slicer settings before sharing

A project file from your slicer contains your printer name, filament settings and sometimes the file path from your computer. If you want to share only the geometry, re-export: in PrusaSlicer, File > Export > Export Plate as STL then import that STL into a new project, or use the 3MF to STL converter and share the STL. Bambu Studio's Export > Export Generic 3MF writes a plain 3MF without the Bambu-specific metadata.

When a 3MF will not open

• "File is not a valid 3MF" or "Unable to read zip". The download was truncated or the file was saved from a browser that mangled it. Check the file size against the source. A healthy 3MF starts with the bytes PK (ZIP signature); if a text editor shows HTML instead, you downloaded an error page.
• Sliced 3MF from Bambu Studio opens with no editable objects. A plate exported with G-code is meant for the printer, not for editing. Ask for the unsliced project, or extract the meshes with a converter; the mesh data is still inside unless the exporter was told to drop it.
• Empty plate after import. Usually a 3MF that uses components referencing objects in external .model files (Bambu, some CAD exporters). Use a reader that follows those references.
• Objects stacked at the origin. The reader ignored the build transforms. The 3MF viewer applies them, which tells you whether the file or the other program is at fault.
• Wrong size. The unit attribute was set to inch or metre by the exporter. Most slicers honour it; some older tools do not. Check the bounding box after import.
• Microsoft 3D Builder refuses a slicer project. 3D Builder is strict about the specification and some slicer extensions trip it up. Open in a slicer instead.

Creating a 3MF

Any current slicer saves its project as 3MF. From CAD: Fusion 360 (File > Export, 3MF), SolidWorks (Save As, 3MF, with options for colour and units), Onshape (Export, 3MF), FreeCAD (File > Export). From a mesh, the STL to 3MF converter wraps the triangles in a package with millimetre units and a shared vertex list, which also compresses the file to roughly a quarter of the binary STL size.

FAQ

Can I open a Bambu Studio 3MF in PrusaSlicer?

Yes, the meshes, names and plate positions load. Filament profiles, process settings and painted supports do not transfer because they are stored in Bambu-specific files inside the package.

Is 3MF the same as STL?

No. STL is a bare triangle list with no units or metadata. 3MF is a ZIP package containing an XML mesh plus units, colours, object names and optionally slicer settings. A 3MF can always be converted to STL; the reverse produces a minimal 3MF with no settings.

How do I view a 3MF without installing a slicer?

On Windows, double-click to open in 3D Viewer. On any platform, drop it into the browser-based 3MF viewer, which runs locally and shows all objects with their plate positions.

Why is my 3MF so much smaller than the STL?

3MF stores each vertex once and compresses the XML with ZIP deflate. A 50 MB binary STL typically becomes a 10 to 15 MB 3MF with identical geometry.

Can a 3MF contain G-code?

Bambu Studio and Orca Slicer can export a "sliced" 3MF that includes G-code for each plate. It is intended for sending to the printer. Other slicers do not store G-code in 3MF.