B-rep solid models vs mesh models
A B-rep (boundary representation) solid describes a part as exact surfaces and edges that enclose a volume. A mesh approximates the surface with triangles. STEP and IGES files normally carry B-rep geometry. STL files carry a triangle mesh.
| B-rep solid | Mesh | |
|---|---|---|
| Surface | Exact surfaces and edges | Flat triangles that approximate the shape |
| Typical files | STEP, IGES | STL, 3MF, GLB |
| Editing in CAD | Faces, edges and holes can be selected and changed | Hard to edit. Features are lost in the triangles |
| Machining and drawings | Suited to CNC programming and dimensioned drawings | Poorly suited. Curved faces are faceted |
| 3D printing and viewing | Usually converted to a mesh first | Used directly by slicers and viewers |
Which one do you need?
- Send STEP when someone will machine the part, edit it, or put it in an assembly.
- Send STL or 3MF when the next step is a 3D printer.
- Use a mesh when you only need a quick look at the shape.
How NitoCAD uses both
The free preview is an STL mesh, so you can see the part before you commit. In CAD Studio, NitoCAD builds a true B-rep solid on OpenCASCADE and exports STEP and IGES for CAD and CAM work, DXF and PDF for drawings, and STL, 3MF and GLB when you need a mesh. See all export formats.
Converting a mesh back into an editable solid is a hard problem and rarely gives clean results. Starting from a B-rep solid avoids it.