3D models come in two fundamentally different representations. Meshes describe a surface as thousands of flat triangles. B-rep solids describe it as exact mathematical surfaces with topology. Knowing which you're working with — and when to convert — saves hours of frustration.

Meshes: triangles all the way down

Formats: STL, OBJ, 3MF, GLB/glTF, USDZ. Tools: Blender, Nomad Sculpt, ZBrush. A mesh cylinder is a prism with enough sides to look round. Meshes are:

  • Great for organic shapes, sculpting, games, AR, rendering, and as the final hand-off to a 3D printer's slicer.
  • Weak for precision: there is no "radius" to edit, no exact flat face to measure, and boolean operations degrade the triangulation over time.

B-rep solids: exact geometry

Formats: STEP, IGES, native CAD files. Tools: SolidWorks, Fusion 360, FreeCAD, Onshape, Shapr3D, and OpenShape3D (via the OpenCASCADE kernel). A B-rep cylinder has a true radius and a true axis. Solids are:

  • Great for engineering: exact dimensions, clean booleans, fillets, measurable mass properties, CNC toolpaths.
  • Weak for sculpting free-form organic surfaces quickly.

The typical workflow

  1. Model as a solid while designing — you keep exactness and editability.
  2. Export a mesh at the end — the slicer or game engine tessellates your exact solid into triangles at whatever resolution you choose.

Going the other direction (mesh → solid) is much harder; reverse-engineering triangles back into faces is an unsolved problem in general. Rule of thumb: stay exact as long as you can.

What this means for iPad CAD

Some tablet apps are mesh modelers with CAD-looking interfaces; fine for art, limiting for parts. If you're designing something with dimensions — an enclosure, bracket, adapter, or replacement knob — pick a tool with a real solid kernel. OpenShape3D models in exact B-rep via OpenCASCADE, imports STL meshes when you need to reference one, and exports STL, OBJ, 3MF, GLB, and USDZ for printing, sharing, and AR.