A solid modeling representation where a 3D object is defined by its bounding surfaces (faces), edges, and vertices: the foundation of all parametric CAD solid kernels.
Boundary Representation (B-rep) defines a solid object by the complete set of surfaces that bound its volume. Each face is a bounded surface patch (planar or curved); edges are intersections of two faces; vertices are intersections of three or more edges. The B-rep data structure stores the topology (connectivity) and geometry (mathematical surface type) separately. All major CAD kernels, ACIS (SolidWorks), Parasolid (Fusion 360), OpenCASCADE (FreeCAD), use B-rep as their internal representation.
B-rep enables exact surface mathematics: a cylindrical hole in a part is represented as an exact cylinder, not a tessellated approximation. This means dimensional tolerances are exact at the CAD level regardless of display tessellation. STEP and IGES exchange formats preserve B-rep data between CAD systems. When designing for precision 3D printing (SLA, SLS, MJF), export STEP files to downstream simulation tools rather than STL to preserve exact surface geometry.
B-rep files (STEP, IGES) from different CAD kernels may import with surface gaps due to tolerance differences between kernels: always check 'Geometry → Repair' after import. B-rep healing is non-trivial and may alter surface mathematics. Not all B-rep faces are guaranteed to be manufacturable: a CAD tool can create geometrically valid but physically impossible B-rep solids (zero-thickness walls, negative volumes).
Related terms: NURBS, Parametric Modeling, STL, Tessellation
| Field | 3D design, engineering |
|---|---|
| Also called | Boundary Representation, solid boundary model |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert