Your shape has no thickness. It's just a surface. Faces in SketchUp have no thickness. In order to be considered a solid it needs to have a volume. The Surface Border message is referring to the perimeter of the surface. [image: DGzU_Screenshot-3_26_20215_53_38AM.png] If you want to use Slicer or the Solid Tools, it first needs to have thickness. I used Vector Push/Pull here. [image: cez1_Screenshot-3_26_20215_56_20AM.png]