"Cut up" or better recreated based on the curves that get outlined in an n value n= extrusion height. In other words, the curves drawn on the surface get moved and scaled away from the original surface then create a new surface in the offset distance plus add 4 (or how many describe the shape in question) new resulting surfaces around this offset surface to close the mesh back up. does this make sense? I'll try and make a graphic of the above soon.