Open CASCADE Boundary Representation .brep
A geometry kernel’s internal state, written straight to disk.
What a .brep file holds
A .brep file is Open CASCADE’s own serialisation of a boundary-representation shape, the vertices, edges, faces and underlying surfaces of a solid, dumped verbatim. It is not really an interchange format so much as the internal state of a geometry kernel, which is why you meet it in FreeCAD, in Open CASCADE-based tools, and in code that scripts them.
Commonly seen in: FreeCAD, Open CASCADE, CadQuery, pythonOCC.
| Data | Stored in BREP |
|---|---|
| Geometry | Yes |
| Materials and colour | No |
| Texture maps | No |
| Animation and rigs | No |
| Scene hierarchy | No |
| Read here | Yes |
| Written here | No |
Tested against a real file
The last sweep loaded as1_pe_203.brep from occt-import-js test files through the viewer on this site: 3,848 triangles across 18 meshes and 18 materials, in 2.9 seconds. Every format's result is on the test results page, run 2026-09-08.
Which way is up
BREP is a Z-up format, which most of the rest of 3D is not. Files are read exactly as written and stood up for you in the viewer; the converter has a switch for it, so a model does not arrive in the next program lying on its side.
Convert BREP to another format
Every pairing has a page saying what survives the trip.
Other things to do with a .brep file
Questions about BREP
How do I open a .brep file?
Drop it into the viewer on this site and it opens in the browser, with the scene tree, the materials and the mesh statistics. Nothing is uploaded. If you want it in another program instead, convert it to GLB, which almost everything reads.
Is BREP a good format to archive in?
BREP stores geometry. Anything outside that list will not be in the file at all, so archive the original alongside it if the surfacing or the rig matters.
Does converting BREP lose quality?
Geometry is copied vertex for vertex, so the shape does not degrade. What gets lost is whatever the target format has no field for: convert to STL and the materials go, convert to OBJ and the animation goes. The comparison table on each converter page says exactly which.
Formats that hold the same things
Or go back to the full format reference.