To create a from a zipper (zip) or surface model in CAD software like SOLIDWORKS or Autodesk Fusion , you typically use specific features to "stitch" surfaces together or fill enclosed volumes. SOLIDWORKS
: If you are using Boundary Surfaces to define your shape, look for the "Create solid" checkbox under the "Options and Preview" section at the bottom of the tool's menu.
: If your "zip" is a mesh, right-click the mesh body and select "Convert to Solid" (or use the Mesh to BRep tool). Generating Face Groups first often helps the conversion process . Which CAD software are you using for this specific model?
: Select all the surfaces that form a closed volume. In the Knit Surface PropertyManager, check the box for "Create solid" to merge them into a single solid body.
: You can select multiple solids, surfaces, or planes that intersect. The tool allows you to merge them or create a solid from the enclosed cavity. Autodesk Fusion