Vacuum forming is a simplified version of thermoforming, where a sheet of plastic in various forms of high-impact polystyrene sheet (HIPS) for low impact products, or ABS for bathroom shower trays, and HDPE for exterior vehicle parts, plus various other types of vacuum formable materials) is heated to a forming temperature, stretched onto a single-surface mould, and forced against the mould by a vacuum. This process can be used to form plastic into permanent objects such as turnpike signs and protective covers. Normally draft angles are present in the design of the mould to ease removal of the formed plastic part from the mould.