Thermoforming is a technique that involves heating sheets of PVC prior to insertion into a blister machine. This is typically achieved by passing the sheets between upper and lower heating plates. When a sheet enters a thermoforming blister machine, it is soft and pliable and can be forced to take on the shape of a mold through the application of pressure. In some cases, a mechanical stamp will be used in addition to the application of pressure, particularly when the shape of the mold is difficult or complex.
Cold forming is a technique that does not involve any application of heat. Unlike the thermoforming method that uses clear PVC, this technique uses thin sheets of laminate film that contain aluminum. In order to create packaging out of these sheets, a blister machine will typically use a stamp to force it into a form. The aluminum-based film will tend to stretch and retain the shape after the stamp has been removed. This type of blister pack is typically used to contain pharmaceuticals, since the aluminum-based film tends to prevent moisture from entering the packaging.