Cavity barriers are passive fire protection elements that prevent flames and smoke from spreading. They work by sealing off the gaps in a cavity during a fire. The materials used in cavity barriers are sensitive to fire. Therefore, they provide essential protection whilst also helping to minimise air leakage and heat loss between the external cavity and the separating party wall. Barriers are used to close concealed spaces and prevent penetration of smoke or flame to restrict the movement of fire within a building. Cavity walls and ceiling voids would be considered concealed spaces and fitted with cavity barriers during construction.