Geometry Shell

Geometry Shell gives a surface real thickness: it creates an inner copy offset along the normals, flips its winding, and stitches every open edge shut with a rim. A plane becomes a slab; an open shell becomes a wall.

Offset slides where the thickness sits relative to the original surface: 0 grows inward, 1 outward, 0.5 splits it evenly.

Thick geometry also shadows more honestly than an infinitely thin sheet, which is often the real reason to use it.

• Walls and panels — A plane with thickness reads as architecture rather than as paper.
• Cut-away objects — Slice a solid, then Shell the result for a proper cross-section with wall thickness.
• Better shadows — A thin sheet casts a suspicious shadow; a shelled one does not.
• Vessels — A sliced sphere shelled becomes a bowl with a rim.
• Extruded outlines — Thickness on an open ribbon.

• Thickness larger than the surface's own curvature radius makes the inner copy self-intersect — keep it modest on tight curves.
• Offset 0.5 is the safest default on a curved surface, since it splits the error between inside and outside.
• Shell after Slice, not before, or the cut will expose the hollow.
• Weld after shelling if the rim's seams show.