Xtratherm CavityTherm Full Fill Wall Insulation Board T&G is a polyiso-based full fill cavity solution for masonry walls. Comprising a rigid PIR core, it delivers a very low thermal conductivity rating of just 0.021 W/mK. This makes it a better themal performer than all other full fill cavity PIR solutions on the market. CavityTherm insulation boards have tongue and groove protusions and recesses on all four sides, which means they fit together snugly. This helps to prevent thermal bridging and reduces the impact of wind driven rain. The boards are flanked on either side by gas tight aluminium facings which assist with heat retention. The Xtratherm full fill boards are 1200mm x 450mm in size, and are specifically designed to fit between brick ties installed at traditional spacings. The boards are sold in plastic wrapped packs. Cavity wall insulation boards are used to insulate external cavities where heat retention is the main priority. For insulating internal walls, products like Rockwool RWA45 100mm are used for their sound deadening properties.