Format Guide
OpenCASCADE's native exact-geometry format — precise NURBS topology for FreeCAD and OCC-based tools.
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| Extension | .brep, .brp |
|---|---|
| Full name | Boundary Representation (OpenCASCADE native) |
| Geometry type | Exact solid geometry — NURBS, B-spline, topology |
| Open standard | Yes — OpenCASCADE Technology (OCCT) |
| Supports color | No |
| Supports assemblies | Yes — compound shapes |
| Primary tool | FreeCAD, any OCCT-based application |
BREP (Boundary Representation) in the context of .brep/.brp files refers to OpenCASCADE Technology's (OCCT) native file format for storing exact boundary-representation solid geometry. Boundary representation defines a solid by its bounding surfaces, edges, and vertices, with topological relationships between them. The .brep format stores OCCT's internal geometric representation (NURBS surfaces, B-spline curves, exact topology) in a compact ASCII form. It is used in the open-source CAD ecosystem — particularly FreeCAD, Salome, and any tool built on the OpenCASCADE kernel, which also powers 3D CAD Converter.
FreeCAD uses BREP as an intermediate format for its Part workbench and Shape objects. Exporting to BREP preserves exact geometry for reimport into other OCCT-based tools.
Developers building applications on OpenCASCADE use .brep files to serialize and deserialize solid geometry between processing steps in CAD pipelines and automation scripts.
BREP files are used in FEA preprocessing (Salome, GMSH mesh generation) and computational geometry research because they provide exact topology without tessellation loss.
FreeCAD, Salome, GMSH, and any application built on the OpenCASCADE Technology (OCCT) kernel. 3D CAD Converter reads and writes BREP using OCCT.
Commonly converted to STEP for universal CAD exchange, to STL or 3MF for 3D printing, or to OBJ/glTF for visualization.
BREP holds exact OpenCASCADE geometry, but most software and 3D printers expect STEP or a mesh. 3D CAD Converter opens .brep and .brp files with the OCCT kernel and exports them in three steps.
Add your BREP files
Drag one or more .brep or .brp files into 3D CAD Converter, or point it at a whole folder for batch conversion.
Pick an output format
Choose STEP or IGES to keep exact solid geometry, or STL, OBJ or glTF to create a mesh for 3D printing, rendering or the web.
Set quality and convert
For mesh exports, set the tessellation tolerance to balance smoothness against file size, then click Convert. STEP and IGES stay exact and need no tessellation.
Prefer the command line? The bundled cadconvert CLI converts BREP both ways and in batch:
A smaller --tessellation value (e.g. 0.1 mm) produces smoother curves and a larger mesh; add --units to control the output scale. BREP, STEP and IGES exports stay exact and ignore tessellation.
BREP and STEP both store exact boundary-representation (B-rep) solids — NURBS surfaces, B-spline curves and full topology — with no triangulation. The difference is reach: BREP is OpenCASCADE's native serialization, perfect inside FreeCAD, Salome and other OCCT-based tools, while STEP (ISO 10303) is the universal neutral format every CAD system reads and writes.
Rule of thumb: stay in BREP while you work inside the OpenCASCADE ecosystem, and export to STEP the moment you need to share a model with SolidWorks, CATIA, Fusion 360 or a client. Convert BREP to a mesh only at the very end, for 3D printing or visualisation. Compare the related exact and mesh formats: STEP, IGES, STL.
Most commercial CAD systems do not import .brep directly — it lives mainly in FreeCAD, Salome and OCCT-based software. Convert to STEP for a model anyone can open. 3D CAD Converter does this in one step.
A .brep file is not a mesh or a text drawing — it encodes exact OCCT geometry that only a CAD kernel can interpret. Generic 3D viewers and text editors cannot display it; open it in an OCCT-based tool or convert it first.
Because BREP is exact, it carries no triangles. Before 3D printing or rendering you must tessellate it into STL, OBJ or glTF; choose a fine tolerance for smooth curves or a coarser one for a smaller file.
A .brep file (sometimes .brp) is OpenCASCADE Technology's native boundary-representation format. It stores exact 3D solid geometry — NURBS surfaces, B-spline curves and full topology — in a compact ASCII form. Because OCCT powers FreeCAD, Salome and many open-source CAD tools, .brep is how they serialize exact geometry without tessellation loss.
Open a .brep file in FreeCAD, Salome, GMSH or any application built on the OpenCASCADE kernel. It needs a CAD kernel to read its exact geometry — a text editor or generic 3D viewer cannot interpret it. 3D CAD Converter opens .brep and .brp files directly with OCCT and converts them to STEP, STL, OBJ and glTF.
To share a BREP model with other CAD systems, convert it to STEP — both keep exact solid geometry. To 3D print or render it, convert to STL or OBJ. In 3D CAD Converter, drop the .brep file in and pick a format, or run cadconvert convert -i part.brep -o part.step from the CLI. Whole folders convert with cadconvert batch -i ./in -o ./out -f stl -r.
Yes. 3D CAD Converter offers a free trial that opens .brep and .brp files and exports them to STEP, STL, OBJ, glTF, 3MF and more — including batch folders — with full control over tessellation quality. Both the desktop app and the cadconvert CLI are included.
Yes. BREP stores exact boundary-representation geometry — NURBS surfaces, B-spline curves and precise topology — with no triangulation, so curved surfaces stay mathematically exact. Converting BREP to a mesh like STL or OBJ approximates those surfaces with triangles, so keep the original .brep (or a STEP copy) as your exact master.