Quick answer
A 3MF file is a compressed package, built on the ZIP container, that holds a 3D model as XML. It records the mesh and, unlike STL, the model's units, colors, materials, and how parts are arranged. Slicers often add their own settings to the same file.
- 3MF stands for 3D Manufacturing Format and is maintained by the 3MF Consortium.
- A .3mf file is a ZIP package. Renaming a copy to .zip shows the files inside.
- It can declare units, colors, materials, components, and build layout; STL cannot.
- Slicer project settings are often stored in private extensions that other applications may ignore.
What a 3MF file is
3MF is a file format for 3D printing and other additive manufacturing. The 3MF Consortium, an industry group, publishes the specification openly. The name stands for 3D Manufacturing Format.
A 3MF file is a package: a ZIP archive that follows the Open Packaging Conventions. Inside are mostly XML files plus optional images such as a thumbnail. The main file, normally 3D/3dmodel.model, describes the model: its vertices and triangles, the objects built from them, and where each object sits on the build plate.
What is inside a 3MF package
- Model part
An XML file with the mesh, the objects, and the build items.
- Units
The model declares its unit. The core specification default is millimeter.
- Components and transforms
An object can be built from other objects, each placed with a transform, so one mesh can appear several times without being copied.
- Colors and materials
Base materials, color groups, textures, and other appearance properties, assigned to whole objects or to individual triangles.
- Metadata and thumbnail
A title, the designer, and a preview image.
- Extensions
Optional specifications such as materials and properties, production, slice, and beam lattice, plus private data that individual slicers write.
How it differs from STL
STL stores one triangle surface and nothing else: no units, no colors, no object names. 3MF stores the triangles together with the information a printer or slicer needs to interpret them. The cost is complexity, because each application has to implement the parts of the specification it wants to support.
How to open and inspect one
- Open it in a slicer or viewer
Most current slicers and many CAD and modeling applications read 3MF. Support for color and materials varies, so compare the preview with the source.
- Look inside the package
Copy the file, rename the copy to .zip, and open it with an archive tool. The XML under the 3D folder is readable text.
- Check the units and the objects
Confirm the unit and the number of objects before you scale or edit anything.
- Use a local inspector
The free 3MF Color Inspector on this site lists objects, colors, materials, textures, transforms, and reference integrity in your browser, without uploading the file.
When 3MF is the better choice
Choose 3MF when scale, several parts, color, or material assignments must travel with the file, or when you send a project to a slicer that reads it. STL remains the safer interchange format for a single plain mesh and for software that does not read 3MF.
Whichever you choose, open the exported file in the application you will print from. A valid package can still lose data in a tool that supports only part of the specification.
Common questions
Technical answers and limitations.
What does 3MF stand for?+
3D Manufacturing Format.
Is a 3MF file the same as a ZIP file?+
It is a ZIP archive with a defined structure. A generic archive tool can open the container, but only 3D applications can interpret the model inside.
Which programs open 3MF files?+
Current slicers, many CAD and mesh applications, and 3D viewers read 3MF. How much of the color, material, and project data each one keeps differs, and the 3MF Consortium publishes a compatibility matrix of software and extensions.
Can I convert a 3MF file to STL?+
Yes, most tools export STL. The conversion keeps the triangles and drops the units, colors, materials, and object structure.
Are 3MF files smaller than STL files?+
Often, because the package is compressed and shared geometry can be reused through components. The difference depends on the model and on the tool that wrote the file.
Primary references
Verify the underlying guidance.
Apply these checks in Meshworthy
Inspect the model, review the operation, and verify the export.
Meshworthy applies these checks locally on your Mac and does not upload your model.
Check what a 3MF keeps before you edit it ↗