Vacuum molding or vacuum forming uses air pressure to mold plastic products. Heated sheets of thermoplastic, typically polystyrene, are placed over a mold cavity. Then vacuum pumps remove the air between the sheet and the mold cavity. This causes the heated plastic sheet to be stretched down into the mold conforming to the sides. Common uses for these products are plastic food containers, and truck cab covers. One negative aspect to this type of molding method is the inability to create complex designs. Deep holes and sharp corners are very hard to achieve. A positive aspect to this method is the ability to stretch clear acrylics and keep clarity.