A chilled air pressure box is provided for thermoforming a plastic sheet. The chilled air pressure box comprises a box, a box perimeter, an inlet valve, a compressed air source and a chilled air source. The box has an interior space within the box and defines an inlet opening. The box perimeter is for sealingly interfacing with a vacuum mold. The inlet valve is substantially disposed within the interior space, adjacent and aligned with the inlet opening such that when the inlet valve is closed the inlet opening is substantially sealed and when the inlet valve is opened the inlet opening is not sealed. The compressed air source is capable of pressurizing the interior space with compressed air and interfaces with the box. The chilled air source communicates with the inlet opening.