Vacuum forming is a simplified version of thermoforming, whereby a sheet of plasticis heated to a forming temperature, stretched onto a single-surface mould, and forcedagainst the mold by vacuum. This ensures the sheet is formed into permanent objects such as turnpike signs and protective covers.

Relatively deep parts can be formed if the formable sheet is mechanically or pneumatically stretched prior to bringing it into contact with the mould surface and applying vacuum.

Suitable materials for use in vacuum forming are conventionally thermoplastics. The most common and easiest to use thermoplastic is high impact polystyrene sheeting (HIPS). This is moulded around a wood, structural foam or cast or machined aluminium mould, and can form to almost any shape. Vacuum forming is also appropriate for transparent materials such as acrylic, which are widely used in applications for aerospace such as passenger cabin window canopies for military fixed wing aircraft and compartments for rotary wing aircraft. Vacuum forming is often used in low-level technology classes for an easy way to mould.