Thermoforming is the process of taking a flat sheet of plastic and forming it into a contoured part or shape. This is done by taking a flat sheet of plastic and clamping it into a carriage, heating the sheet in a large oven, stretching the hot sheet over a mold and pulling a vacuum on the cavity to force the sheet to the contour of the mold. At this point in the process the sheet begins to cool with the assistance of fans placed around the mold and the plastic sheet becomes rigid again as it takes the shape of the mold.

There are several variations to thermoforming, including drape forming, pressure forming, and twin sheet forming. Each variation has advantages and disadvantages but the general process is the same.

Additionally there is a wide range of material choices available for thermoforming. These materials include High Density Polyethylene (HDPE), Polypropylene (PP), Acrylonitrile-butadiene-styrene (ABS), Polycarbonate (PC), and Thermoplastic Olefins (TPO). The most common material used for general purpose thermoforming is HDPE.