The 3MF format

A .3mf is a ZIP file full of XML. It holds your models, where they sit on the plate, their colours, and usually the slicer's settings.

Unlike STL, it keeps units, colours, several named objects and their placement. See 3MF against STL.

How do I open one without a slicer?

Drop it on preslice. Or rename it to .zip and open it with any unzip tool. For the answer on a phone, in Blender or in CAD, see how to open a .3mf.

Can a .3mf carry a virus?

It does not run by itself. The risks are slicer bugs and custom G-code; see can a .3mf file have a virus.

Who defines the format?

The 3MF Consortium publishes the 3MF Core Specification. It is also the standard ISO/IEC 25422:2025.

Where do I read more?

• What a .3mf contains: the files and the model tree.
• Print settings in a .3mf: where each slicer puts them.
• Extensions: the optional add-ons.
• 3MF against STL and 3MF against G-code.
• 3MF to STL and STL to 3MF: saving one out, and bringing one in.
• 3MF to OBJ and OBJ to 3MF: saving one out, and bringing one in.
• 3MF to STEP: what Fusion and FreeCAD do with one.