Why 3MF exists
STL has served the 3D printing industry for decades, but its limits show quickly: no units, no colors, no materials, one mesh per file. 3MF (3D Manufacturing Format) was designed by the 3MF Consortium to fix those limits while remaining open and simple to parse.
A 3MF file is a ZIP archive containing XML resources. That means existing ZIP and XML libraries handle most of the work — no custom binary parser is required.
Inside the archive
Every 3MF has a few canonical parts: a /3D/3dmodel.model file holds the geometry and build instructions; /_rels tracks relationships; /Metadata optionally stores thumbnails. Because it is a ZIP, files can also carry slicer extensions — Bambu, PrusaSlicer, and Cura all write their own extension parts.
Geometry is stored as indexed triangle meshes. Unlike STL, vertex positions are shared, which means a 3MF file is often smaller than an equivalent STL once compressed.
Units, colors, and materials
3MF stores units explicitly, so there is no guessing whether a number means millimeters or inches. The format supports named materials and per-triangle or per-vertex colors, and it can reference multiple objects in a single build.
This makes 3MF a better choice for anything beyond a single monochrome mesh — multi-material prints, assemblies, and labeled parts all map cleanly.
Tooling support
Every major slicer reads 3MF. Bambu Studio, PrusaSlicer, Cura, OrcaSlicer, and IdeaMaker all import and export it, often preferring 3MF over STL for project files.
CAD tools on the export side are catching up: Fusion 360, SolidWorks, and Autodesk Inventor all produce 3MF; FreeCAD has plugin-based support.
Viewing 3MF in STLViewer
STLViewer parses the mesh parts of a 3MF archive and renders them exactly like an STL model — geometry only. Slicer-specific extensions (support structures, print settings) are ignored.
If you need to inspect a print job quickly before committing to a slice, dropping the 3MF directly into STLViewer is faster than opening a slicer — and you can share the result with a single link.