Free online X3D to BREP converter

What the X3D format is

X3D is an XML-based format for 3D scenes, descended from VRML. It stores polygon meshes, materials, colors, textures, lights, cameras, transforms, and animation data rather than native CAD features such as sketches, fillets, or parametric constraints.

Web3D tools, simulation packages, 3D viewers, CAD export utilities, Blender, and scientific visualization software can create X3D files. You may encounter .x3d files when exporting interactive models, sharing Web3D scenes, or moving geometry from visualization software into another application.

An X3D file can contain several independently transformed objects. It can also use external textures, indexed polygon faces, normals, transparency, and scene elements that have no equivalent in a BREP model.

What the BREP format is

BREP, or boundary representation, describes a model through topological entities such as vertices, edges, wires, faces, shells, and solids. The commonly used .brep or .brp form is associated with OpenCASCADE and is supported by applications including FreeCAD and other CAD systems based on OpenCASCADE Technology.

BREP is useful for checking solid validity, measuring faces and edges, performing Boolean operations, and exchanging geometry between CAD applications. It can preserve mathematically defined faces when the source contains them, but an X3D mesh normally provides only polygonal surfaces.

How to convert X3D to BREP

FreeCAD is a practical desktop option because it can import mesh geometry, convert a mesh into a Part shape, and export the resulting shape as BREP.

1. Open FreeCAD and choose File → Open, then select the .x3d file. If the importer does not appear to accept the file, use the Mesh workbench and its import command instead.
2. Inspect the imported object in the 3D view. Confirm that the scale, orientation, object placement, and number of mesh components are correct. X3D cameras, lights, animations, and materials are not needed for BREP export.
3. Switch to the Part workbench and select the mesh object in the model tree.
4. Choose Part → Create shape from mesh. Set a tolerance appropriate to the model units. A smaller tolerance retains more detail but can increase processing time and may expose defects in a badly triangulated mesh.
5. Select the generated shape and use Part → Refine shape if duplicate or unnecessary seam edges need removal. Do not use refinement as a substitute for repairing holes or self-intersections.
6. Check the result with the Part workbench validation tools. A valid solid should have closed shells and no missing faces, open edges, or self-intersections.
7. Choose File → Export, select the generated Part shape, and save it with a .brep extension. If FreeCAD offers several BREP-related filters, choose the OpenCASCADE BREP option rather than a mesh format.

For repeated conversions, the same process can be automated with FreeCAD's Python console using its Mesh, MeshPart, and Part modules. The exact scripting API varies by FreeCAD version, so the graphical workflow is preferable when tolerance and repair decisions must be inspected interactively.

You can also convert the file on 101convert.com for free without installing software. Online processing is most suitable for uncomplicated, publicly shareable models; use desktop software when the file contains confidential geometry or requires repair and validation.

Quality and compatibility limitations

Mesh-to-BREP conversion does not recreate parametric CAD geometry. Triangles in the X3D file generally become planar BREP faces. A curved object exported as a dense mesh remains a faceted model, even though the output uses a CAD boundary-representation container.

The X3D mesh must usually be watertight, consistently oriented, and free of duplicate vertices, zero-area triangles, non-manifold edges, and self-intersections. An open surface may export as a shell rather than a usable solid, and a damaged mesh may fail during shape creation.

Scene transforms can affect location and scale, while unit metadata is not consistently handled across X3D producers. Verify dimensions after import and before export. Textures, colors, lights, cameras, animation, and other presentation data are normally discarded; BREP stores geometry and topology, not the complete X3D scene.

BREP implementations are not completely interchangeable. Confirm that the receiving CAD system supports the OpenCASCADE BREP variant and test the exported file by reopening it and checking solids, face count, dimensions, and required Boolean operations.