Thermorforming consists of a group of forming method in which a thermoplastic sheet is heat softened and then (in the majority of cases) formed into an open mould as a core and or a cavity using pressure or suction. The principle is the same in both these processes, but the latter is the more common technique and is referred to as vaccum forming. It is mainly used in the packaging industry to make location trays for confectionery, cosmetics, electrical goods, and so on, but it can also be used for larger structural items such as boat hulls, inside door panels for refrigerators and baths or shower cubicles etc.

The principle of the process is simple. The plastic sheet is clamped over an open mould where it is heated until soft. The heater is then removed and the air is evacuated from between the sheet and the mould so that the atmospheric pressure above the sheets pushes it down into the mould. Cold air may then be blown on to the sheet to cool it quickly and ensures that it retains the contours of the mould. Trimming is usually required to remove excess material.

A potential problem in this simple version of the process is the redistribution of material after heating the sheet that it should not bottom thin at the bottom corners of the moulding. To improve the wall thickness distribution, modification can be made to the basic process, for example, using drape forming over a male die or using a plug to push the softened sheet down into the mould before the vaccum is applied.

In practice the vaccum forming equipment is often part of complete production line. Typically, at the beginning of the line, pellets are extruded to produce the plastic sheet or in some cases the plastic disc required for forming. After shaping on the vaccum machine the containers have printing added and they are then filled with, say, diary produce before being packed for distribution. The familiar blister packs which are currently being wldely used in packaging of medicine and other food products is going to attract consumers because of its better appearance. Skin packing is also useful because of its abililty to pack any odd shape. Blister packs and skin packs are also made by vaccum forming. The most suitable materials for thermoforming are polystyrene (rubber toughened or expanded grades, ABS, polyvinyl chloride (special grades), acrylic, CAB, and polycarbonate. Since only low pressure are involved in thermoforming, mould may be made from wood or plaster (for protypes) of metal filled epoxy, steel, or alluminium (for protection) *Above all materials HIPS has lower oxygen and water permiability which gives more exposure to be processed through vaccum forming. Multilayer sheets are also fed for the processed food and pesticides packing for longer life.*

Other than those products mentioned earlier, thermoforming may be used to produce egg cartoons, light covers, vehicle body panels, sink units shelters, advertising signs, deep freezer liners, face masks, disposal cups and numerous car components.