Thermoforming describes the process of heating a thermoplastic sheet to its softening point, stretching it over or into a single-sided mold and holding it in place while it cools and solidifies into the desired shape. The thermoplastic sheet is clamped into a holding device and heated by an oven using either convection or radiant heat until it is softened.

The sheet is then held horizontally over a mold and pressed into or stretched over the mold using vacuum pressure, air pressure or mechanical force. The softened sheet conforms to the shape of the mold and is held in place until it cools. The excess material is then trimmed away and the formed part is released. This material can be reground, mixed with unused plastic and reformed into thermoplastic sheets.

Thermoforming is commonly used for food packaging, but it’s also used in other applications that vary from plastic toys, aircraft windscreens to cafeteria trays.

Thin-gauge (less than 0.15 cm) sheets are mostly used for rigid or disposable packaging, while thick-gauge (greater than 0.3 cm) sheets are typically used for cosmetic permanent surfaces on automobiles, shower enclosures and electronic equipment.

A variety of thermoplastic material can be used in this process, including the following:
- Resin used
- Acrylic (PMMA); Acrylonitrile Butadiene Styrene (ABS)
- Low Density Polyethylene (LDPE)
- High Density Polyethylene (HDPE)
- Polypropylene (PP)
- Polystyrene (PS)