Cavity Shield is a retrofit cavity wall insulation product designed for new and existing homes. Made from polystyrene, it is pumped between your double bricks into the cavity. Up to 25% of your heat transfer occurs through your wall. Cavity Shield improves the wall thermal performance from R0.4 to R2; a 400% increase. Being polystyrene, this is no different to how an esky or thermos works – only this is around your home. It does not hold water and remains breathable, so your cavity doesn’t hold moisture. Supplied and installed same day, the average home can be installed from $2,700.