What Is a 3MF File?
A 3MF file is the modern container format for 3D printing. Where STL stores only a bare triangle mesh with no units, no color, and no print settings, 3MF stores all of that in one tidy package — and slicers read it better for it. Here is what the format actually contains, how it compares to STL, and when to export one.
What a 3MF file stores
3MF is a ZIP archive containing an XML file that describes the part. Inside it can carry:
- Geometry — the triangle mesh, same as STL.
- Units — millimeters explicit in the file (STL has no units; the slicer guesses).
- Color and material properties — per-face or per-object colors; multi-material part assignments.
- Print settings — layer height, support preferences, infill; slicer profiles some vendors embed.
- Metadata — designer name, application, creation date.
- Thumbnails — a preview image modern slicers display in the file browser.
The result is a richer handoff to a slicer. No more “is this in mm or inches?” — that is encoded. No more manually assigning colors to objects after import.
3MF vs STL — the plain difference
STL
Invented in 1987. Stores only triangles — no units, no color, no metadata. The slicer assumes the units (usually mm for modern exports). Universal support, but bare-minimum information. Some slicers still scale STL files incorrectly if the export used inches.
3MF
Published by the 3MF Consortium in 2015. Carries units, color, materials, and settings. Smaller file size than binary STL for the same geometry (better compression). Supported by PrusaSlicer, Bambu Studio, Cura, Chitubox, and most major slicers from 2018 onward.
For 3D printing in 2026, 3MF is the better default when your slicer supports it. STL is still fine for simple single-color parts and for maximum compatibility with older or unfamiliar tools. See the full comparison in STL vs 3MF: which to export.
Neither 3MF nor STL is the right format for CNC machining or editing in another CAD tool — those need STEP. See STL vs STEP: which file format.
How to open a 3MF file
Any modern 3D printing slicer reads 3MF:
- PrusaSlicer / SuperSlicer — File → Import → Import 3MF/AMF.
- Bambu Studio — drag and drop; the whole print project (part + settings) can be a single .3mf.
- Ultimaker Cura — Open file; 3MF supported natively.
- Windows 3D Viewer — built into Windows 10/11, opens .3mf directly.
- macOS Preview / Quick Look — does not natively render 3MF; use a slicer instead.
If you want to edit the underlying geometry (not just slice it), import the 3MF into a CAD tool that accepts mesh input. For editable solid geometry, export as STEP instead — see what is a STEP file.
Export a 3MF from PartWork.ai
After generating a part in PartWork.ai, choose 3MF from the export menu. The file includes the mesh geometry with millimeter units set correctly — ready to drag into PrusaSlicer, Bambu Studio, or Cura. For full details on export formats and what each is good for, see exporting files.
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