All our vapor caps vaporize identically and share the same internal parts. The Lotus rings on the top of the caps are stainless steel and are either bare or covered with a black, baked on ceramic coating. The black rings are coated for visual appeal only and are functionally the same as the bare rings.
The Saucer cap has a raised edge to provide an extra layer of protection for fingers that might come in contact with a hot Lotus ring or hot plate. It also gives some protection to the hot plate during storage.