Abstract: An apparatus for thermoforming plastic sheet material which has a frame and complementary mold halves mounted on the frame for movement toward and away from one another. The apparatus has an indexing means which moves along a vertical path to pull the plastic material through the mold and a clamping means disposed between the mold halves which operates with the mold to clamp the plastic sheet around the edges of the forming tool of one mold half. The indexing means and clamping means operate to reduce sag of the plastic material and improve uniformity of the finished article. Operation of the apparatus is enhanced by the use of air pressure, vacuum and cooling during molding and release.