Free online FBX to BREP converter

FBX files are common in animation and game workflows, while CAD systems often require boundary-representation geometry for precise editing and manufacturing. Converting the file is useful when a polygonal FBX model must be opened as a BREP object in Open CASCADE or another solid-modeling system.

What the FBX format is

FBX is a proprietary Autodesk interchange format for 3D scenes. It can contain polygon meshes, object transforms, materials, textures, cameras, lights, skeletons, animation takes, and skinning data.

Autodesk Maya, 3ds Max, MotionBuilder, Blender, Unity, Unreal Engine pipelines, and many digital-content applications create or import FBX files. You commonly encounter it when receiving an animated asset, exporting a character or environment from a game workflow, or transferring geometry between modeling and visualization software.

FBX is primarily a scene and polygon-mesh format, not a mechanical CAD solid format. Its meshes do not normally contain analytic planes, cylinders, fillets, parametric constraints, or the topological information required for direct solid editing.

What the BREP format is

BREP means boundary representation. A BREP model describes a solid or surface through topological entities such as vertices, edges, wires, faces, shells, and solids, together with the geometric surfaces underlying those entities.

The .brep extension is commonly associated with the Open CASCADE BREP file format, although BREP is also used as a general description of boundary-representation geometry. Open CASCADE-based applications can store exact planar, cylindrical, conical, spherical, and free-form faces instead of only storing triangles.

BREP is appropriate for CAD inspection, Boolean operations, sectioning, mass-property calculations, and precise surface or solid editing. It is not automatically a parametric model: converting a mesh to BREP does not recreate the original feature tree, sketches, dimensions, or design history.

How to actually convert FBX to BREP

Method 1: Convert the FBX to a faceted BREP with Blender and FreeCAD

1. Open the FBX in Blender with File → Import → FBX (.fbx).
2. Delete cameras, lights, armatures, and hidden objects if only the model geometry is required. Apply object transforms with Object → Apply → All Transforms.
3. Select the required mesh objects and export them as STL with File → Export → STL. Use the scene units and a sufficiently fine tessellation; STL preserves triangles but not materials, animation, or exact CAD surfaces.
4. Open FreeCAD and import the STL with File → Import. In the Python console, create a BREP shell from the imported mesh:

import FreeCAD as App, Mesh, Part
mesh = Mesh.Mesh('model.stl')
faces = []
for facet in mesh.Facets:
    points = [App.Vector(v) for v in facet.Points]
    wire = Part.makePolygon(points + [points[0]])
    faces.append(Part.Face(wire))
shell = Part.makeShell(faces)
doc = App.newDocument('Converted')
obj = doc.addObject('Part::Feature', 'BREP')
obj.Shape = shell
doc.recompute()
Part.export([obj], 'model.brep')

Replace model.stl and model.brep with full paths when the files are not in FreeCAD's working directory. The result is an Open CASCADE BREP containing planar triangular faces. If the mesh is closed and consistently oriented, attempt to create a solid before exporting:

solid = Part.makeSolid(shell)
obj.Shape = solid

If Part.makeSolid fails, the mesh has gaps, non-manifold edges, duplicate faces, or inconsistent face directions. Repair the mesh in Blender or a mesh-repair tool, then repeat the export.

Method 2: Use a CAD translator

A commercial CAD translator that explicitly lists both FBX import and Open CASCADE BREP export can perform the intermediate tessellation and file writing in one workflow. Import the FBX, select only the required geometry, inspect units and object scale, then choose the application’s BREP or Open CASCADE export command. Confirm that the output is a solid rather than a collection of open faces.

On 101convert.com, use the converter interface to select FBX as the source and BREP as the output when those formats are available. This requires no installed software, but the output should still be opened in a BREP-capable CAD application and checked for gaps, incorrect scale, and unwanted separate objects.

Quality, compatibility, and limitations

• Mesh conversion is not surface reconstruction. The FreeCAD workflow produces one planar BREP face per source triangle. It does not infer smooth cylinders, NURBS patches, fillets, or design intent.
• Resolution controls file size and appearance. A dense FBX mesh creates a large BREP with many faces; a coarse mesh creates visible faceting and inaccurate measurements. Preserve the original FBX and STL because the BREP cannot recover discarded detail.
• Units require verification. FBX unit metadata is inconsistently interpreted by applications, and STL has no standard unit declaration. Confirm a known model dimension after import and scale before BREP export.
• Scene data is lost. Materials, textures, animation, skinning, cameras, lights, and hierarchy do not belong to the resulting solid unless the target application stores them separately.
• File extensions are implementation-dependent. A BREP written by Open CASCADE may not open in a system expecting another vendor’s BREP dialect. STEP or Parasolid is often a better exchange format when the receiving CAD system supports it.
• Watertightness matters. A closed, manifold, consistently oriented mesh can become a solid; an open or self-intersecting mesh remains a surface shell or fails during solid creation.