Free online 3MF to BREP converter

What the 3MF format is

3MF is a ZIP-based 3D-printing container defined by the 3MF Consortium. Its XML data describes one or more triangle meshes, while the package can also contain materials, colors, textures, build placement, thumbnails, and printer-related metadata.

PrusaSlicer, OrcaSlicer, Bambu Studio, Ultimaker Cura, Microsoft 3D Builder, Fusion, SolidWorks, Blender, and other CAD or slicing applications can create or export 3MF files. You commonly encounter 3MF when downloading a printable model, moving a prepared build between slicers, or exporting a design for additive manufacturing.

What the BREP format is

BREP, or boundary representation, describes a model through topological entities such as solids, shells, faces, edges, and vertices, together with the geometric surfaces and curves that define them. The .brep extension commonly refers to the Open CASCADE BREP format, although some applications use different BREP-based extensions.

BREP is intended for CAD operations such as boolean cuts, fillets, face selection, sectioning, measurement, and precise solid validation. Unlike a triangle mesh, a native CAD BREP can store analytical planes, cylinders, cones, and parametric surfaces. A 3MF-to-BREP conversion normally creates a faceted BREP from the mesh; it does not recreate the original feature tree or exact design intent.

How to actually convert 3MF to BREP

Using FreeCAD

1. Install a recent version of FreeCAD and open the Mesh workbench.
2. Choose File → Open and select the .3mf file. If your FreeCAD build does not provide 3MF support, export the model from the slicer as .stl or .obj, then open that mesh instead.
3. Inspect the imported mesh for holes, self-intersections, duplicate faces, inverted normals, and disconnected shells. Use the Mesh workbench repair and analysis tools before conversion.
4. Select the mesh object and choose Meshes → Create shape from mesh or the equivalent command in your FreeCAD version. Set a deviation or tolerance appropriate to the model: a smaller value follows the triangles more closely but may create a heavier BREP.
5. Switch to the Part workbench. Select the generated shape and use Part → Refine shape when coplanar or coincident edges need cleanup.
6. If the result is a closed shell rather than a solid, select the shell and use Part → Convert to solid. FreeCAD may refuse this operation when the mesh contains gaps, non-manifold edges, or intersecting faces.
7. Select the final shape and choose File → Export. Enter a filename ending in .brep or .brp, then select the BREP/Open CASCADE format offered by the file-type list.

For repeatable processing, the same workflow can be performed through FreeCAD's Python console, but the exact mesh-import and conversion API depends on the FreeCAD release and installed format support. The graphical workflow is safer when the source contains multiple objects or invalid shells.

Using the online converter

For a one-off conversion without installing software, upload the file to 101convert.com, choose BREP as the output format, run the conversion, and download the resulting file. Check the output in the target CAD program because online converters may reject large packages, omit 3MF metadata, or produce a faceted shell that is not a valid solid.

Quality, compatibility, and limitations

• Mesh geometry is retained as facets. A dense 3MF mesh can produce a large BREP with thousands or millions of triangular faces.
• Exact CAD surfaces are not recovered. Cylinders, planes, fillets, and other surfaces remain triangulated unless a separate reverse-engineering or surface-fitting operation replaces them with analytic geometry.
• 3MF scene data may be lost. Colors, materials, textures, print profiles, build plates, thumbnails, and object placement may not exist in the exported BREP.
• Watertightness matters. A mesh with open boundaries or non-manifold geometry may convert only to a shell, or fail when converted to a solid. Repair the mesh before export.
• BREP dialects differ. Confirm that the receiving program supports Open CASCADE .brep/.brp; a program requiring Parasolid, ACIS SAT, STEP, or IGES will need that specific export format instead.
• Tolerance affects downstream operations. Excessive deviation can alter dimensions, while an unnecessarily strict tolerance increases file size and may expose tiny defects that prevent booleans or solid validation.