Vacuum forming operation involves the drawing the of plastic film (usually from reel stock) under the clamp frame and heating the plastic until softened. The mould is then raised and vacuum applied to draw the softened plastic onto the mould. Air can be injected under the softened sheet so that it will rise in the clamp frame and form a bubble. This pre-stretches the material evenly before being drawn over the film (and also to keep the material sagging onto the lower heater). The formed sheet is then cooled; the formed sheet is removed. The processing cycle is automatic.

Machines with double heaters are generally used for Vacuum Forming thick sheets (for 3 - 10mm).