A CAD operation that removes the interior of a solid, leaving a uniform-thickness hollow shell, or equivalently removes selected faces to create an open-top box.
Shell (also called hollow) offsets all surfaces of a solid inward by a defined wall thickness t, removing the interior volume. One or more faces can be selected as 'open' faces to be removed entirely, leaving an opening (like the top of a box). The result is a thin-walled hollow body. Available in all major CAD tools (Shell feature in SolidWorks/Fusion 360, Hollow in FreeCAD).
Shelling drastically reduces material use and print time for bulky models. For FDM, shell at 2–4× nozzle diameter (e.g., 0.8–1.6mm for 0.4mm nozzle) creates printable walls with infill-free interiors. Combined with drain holes (boolean difference), shelled SLA/resin parts avoid trapped resin pools that can crack during post-cure. For Bambu Lab printers, shelling before export and setting low infill in the slicer gives best weight/strength ratio.
Shell operations fail when wall thickness t is too large relative to small features: the offset surfaces self-intersect. Features like bosses or ribs thinner than t will be consumed by the shell. Always validate the shell result with a cross-section plane. Non-manifold input geometry (before shelling) causes immediate failure: fix mesh first.
Related terms: Wall Thickness, Boolean Operation, Manifold Geometry
| Field | 3D design, 3D printing |
|---|---|
| Also called | shelling, hollow body, thin-wall |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert