About Surface Data
It is best to import solid models from second generation CAD systems as surfaces.
You can construct a solid from the imported surface data in several ways depending on the information available in the imported feature. A solid can be created automatically out of the imported data during the import process if Creo has sufficient data, for example, closed quilts. The system tries to create a solid protrusion if the imported data contains closed quilts.
If the imported geometry contains surfaces that are not connected, the imported feature appears as a collection of quilts or a quilt with gaps. After import, convert the imported feature into a solid.