Expanded polystyrene can be used as permanent formwork, either to provide thermal insulation, for example, under floors and ground beams, or to form voids in large members. The most common voids are in bridge decks or structural slabs. The material can easily cut or trimmed to the required shape.

Although not strictly a permanent formwork application, expanded polystyrene can be readily dissolved using special solvent-emulsifiers; the residue can be washed off or wiped away with a cloth. Thus expanded polystyrene may be used in situations where formwork must be removed but access would prevent the striking of conventional formwork.

SAFETY WARNINGS: Expanded polystyrene is combustible and care should be taken in its storage and use, particularly if welding or burning operations are taking place in close proximity.

The solvents used are likely to be highly flammable and may be potentially damaging to the environment. They should only be used strictly in accordance with the manufacturer´s recommendations; operatives should wear appropriate protective clothing.