Cavity liner for use with air bricks to form a duct through walls to assist ventilation. Free air space 4624mm2 Suitable for new build and refurbishment projects Red colour resistant to fading Resistant to frost and the freeze/thaw cycle. The Cavity Liners are used alongside airbricks to allow much-needed ventilation within cavity walls. Ideal at providing a bridge to air bricks letting air flow freely around the cavity wall, reducing the chances of gas or damp building up.