You don't need to 'edit' a group to change its entities. So once you have an array of the newly 'grouped_faces' [made as you group them] just process it thus: thick=1.0 ### or whatever dim desired grouped_faces.each{|group| group.entities.to_a.each{|e| next unless e.is_a?(Sketchup;;Face) e.pushpull(-thick) ### -ve pushes against face.normal } }