Twin sheet forming is commonly used to produce hollow products as an alternative to blow molding or rotational molding. Two sheets of plastic are fed between halves of an open mold. A blow pin is introduced and the mold halves are closed. The sheets are formed to the walls of the mold by vacuum and air pressure. The mold halves open and the part is released. Twin sheet forming provides opportunities for gains in structural strength which are not obtainable using single sheet thermoforming. Able Mfg. can also fill the hollow cavity with expandable foam for greater rigidity.