The Hepworth Terracotta Cavity Liner is for use with air bricks to form a duct through exterior walls to assist the ventilation of floor and roof voids. The product measures 215 x 65 x 200mm (D x W x H) approx. and is suitable for new build and refurbishment projects. Manufactured from vitrified clay which is a natural and durable product. Its weight is 4kg and is used in conjunction with 215 x 65mm (W x H) airbricks. The Cavity Liner is resistant to frost and fading.