Siderise RH ‘Open State’ horizontal cavity barriers consist of a non-combustible stone wool lamella core, with reinforced aluminium foil faces. This primary seal has a reaction to fire performance to Class ‘A1’. The exposed leading edge is also sealed with aluminium foil. Whilst the base material is water repellent and non-hygroscopic, this predominantly enclosed arrangement affords an added degree of weather protection to the core material.

The intumescent material has a reaction to fire performance to Class ‘E’. In the event of exposure to fire, the intumescent rapidly expands and fully seals the purposely designed ventilation gap formed at the time of installation, between the barrier and the rear of the cladding.