hidden surfaces INGAME are hidden, however, im compiling a test map right now for a way im trying to make terrain, the map, though small, was using over 6000 numportals, so after reading your post, i desided to try and appy the skip texture anyway, to brush faces, insead of the entire brush, this helped greatly, because what it did was knock the numportals down, due to the fact that is skips them in compile, instead of skipping faces ingame, so it saves compile time without appying the skip to everywhere i could, i still dropped the portals down to just above 4000