: Select a group of intersecting surfaces or polysurfaces that "box in" a volume. Rhino will trim the excess and join the pieces into a single closed solid.

Version is a specific Service Release Candidate (RC). While it includes standard bug fixes and stability improvements, the fundamental solid-modeling engine remains consistent with the main Rhino 7 documentation. Create a Solid with Rhino 7 or 8

: When extruding a closed curve (like a circle or square), ensure the Solid=Yes option is selected in the command line to create caps at both ends. Verification Tools

: If you have a planar opening (a flat hole) in a polysurface, the Cap command will create a flat surface to seal it and turn it into a solid.

: Run this and select Naked Edges . If any edges highlight in magenta, your object is not yet a solid and has gaps that need to be closed.