3MF File

What a 3MF file is

3MF comes from the 3MF Consortium, an industry group formed in 2015 that built on 3D printing format work by companies including Microsoft and HP. The specification is free to implement, and in 2025 it was published as an international standard, ISO/IEC 25422:2025.

A 3MF file is a ZIP package that follows the Open Packaging Conventions. Inside are XML parts: the main 3D model, plus optional thumbnails, textures, and print settings. Renaming a .3mf file to .zip lets you open it and look inside.

What 3MF stores that STL does not

The 3MF Consortium sums up the difference this way: STL has no colour or material information and no way to add it, and because it does not store how triangles connect, it produces larger files and can lose manifoldness through rounding errors.

Geometry rules

The core specification defines exactly what a valid mesh is. In a mesh that defines a solid part, every triangle edge is shared with exactly one other triangle, neighbouring triangles face the same way, and each triangle's corners are listed counter-clockwise so its normal points out of the part. The specification also fixes how overlapping or self-intersecting shapes are read, so conforming programs interpret a file the same way.

Each object also has a type, such as model, support, or solid support, so a file can keep the part separate from support structures. The rules only help when the exporting program follows them, so still check the file in a slicer before printing.

Model files and project files

CAD programs export 3MF as a model file: geometry, units, and object names. Slicers use the same container for project files. A PrusaSlicer project, for example, saves every object with its print settings and modifiers, so a job can be reopened exactly as it was. Much of that project data is written by and for the program that saved it, so other programs may read only the geometry.

When to use 3MF

• Printing several parts at once, where object names and positions should travel together.
• Colour or multi-material prints, which STL cannot describe.
• Any print where the unit should be stated in the file rather than assumed.
• Not CNC machining. 3MF stores surfaces as triangle meshes and does not support exact curved surfaces such as NURBS; the consortium itself points to STEP and IGES for CNC work.

Exporting a good 3MF

1. Export from the original CAD model, as closed solid bodies.
2. Check the unit in the export dialog, even though 3MF records it.
3. Choose a fine resolution. 3MF is still a triangle mesh, so curves are approximated by flat facets just as in STL.
4. Give each part a clear name, and export only the parts you want made.
5. Open the file in a slicer to check its size, parts, and orientation.