Thermoforming is a molding process used to form sheets of plastic to a mold surface by using heat and force consisting of vacuum and/or pressure. This technology appeared to to have applications during the prime of thermoplastics. Thermoforming is a downstream plastic process, however it is often viewed as an alternative to injection molding in numerous markets and end-uses.

Thermoforming is used primarily in low-cost applications for the simple embossing of thin plastic sheet and cannot be used to form as rigid shapes as vacuum forming is capable of. Thermoformed plastics are invariably thermoplastics because thermosetting plastics assume their final shape through heat and so can not be moulded with this process.

Familiar products manufactured by thermoforming include: yoghurt pots and simple trays. The plastics that are used in thermoforming include: acrylic, low density polyethylene (LDPE) and crystalline polyester (CPET).

Images from Seagull, a thermoforming machine maker

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There are three types of thermoforming molds:

Machined Aluminum Molds-- are typically built for shallow parts with small draw ratios. Male or female molds and vacuum-form or pressure-form molds can be machined aluminum molds. They can be textured and may offer features such as loose cores, pneumatic cores, and inserts.

Cast Aluminum Molds -- are cast at a foundry from a machined pattern from a composite material and typically are built for parts with large draw ratios

Composite Molds --For prototyping and short production runs, cost-efficient composite materials are used for mold construction. These molds produce parts that are to be evaluated for fit, form, and function and may be modified to evaluate possible design changes. These molds are for vacuum-forming only and are not temperature controlled. These molds have a limited life.