The sheet or film is heated between infrared, natural gas, or other heaters to its forming temperature. Then it is stretched over or into a temperature-controlled, single-surface mold. Cast or machined aluminum is the most common mold material, although epoxy and wood tooling are sometime used for low volume production. There are several categories of thermoforming, including vacuum forming, pressure forming, twin-sheet forming, drape forming, free blowing, and simple sheet bending.

Vacuum forming, commonly known as vacuforming, is a simplified version of thermoforming, whereby a sheet of plastic is heated to a forming temperature, stretched onto or into a single-surface mold, and held against the mold by applying vacuum between the mold surface and the sheet. Thermoforming has close similarities with vacuum forming except that greater use is made of air pressure and plug assisted forming of the softened sheet. The process in thermoforming is invariably automated and faster cycle times are achieved than in the vacuum forming process. Only thermoplastics sheet can be processed by this method. The vacuum forming process can be used to make product packaging, speaker casings and even car dashboards.

The majority of thermoforming production is by roll fed machines. Sheet fed machines are used for the smaller volume applications. Larger production units have in house sheet extrusion equipment. Many thermoplastics can be thermoformed, which include polystyrene, polypropylene, apet, cpet, and pvc. Evoh is commonly incorporated into a co-extrusion for its superior barrier properties in food. For non-demanding applications, a mono material thermoplastics sheet is usually specified. This is a sheet in which there is only one material. With a more demanding application, a multi-layer thermoplastics sheet is used. Multi head extruders feed into the extrusion die with the differing materials.

Thermoforming process provides products that are largely used for food packaging. Other industries use thermoformed articles include toiletries, pharmaceuticals and electronics. The modern food supply chain uses many forms of thermoformed articles. Meat trays, microwave & deep freeze containers, ice cream and margarine tubs, delicatessen tubs, snack tubs, bakery and patisserie packaging, sandwich packs and vending drink cups are just a few of the food related applications. Other non-food applications of thermoformed articles include manufacturing collation trays, wood lamination, blister packaging and point of sale display trays.