Rockwool® Cavity Insulation Is A Semi-Rigid, Full-Fill Insulation Solution For Masonry Cavity Wall Construction, Suitable For Use In New Builds Or Extensions. Lightweight And Easy To Handle, The Batts Are Simple To Install And Provide A Close Fit Against Brick And Blockwork. Rockwool Cavity Full Fill Insulation Batts Are Non-Combustible And Contain Water Repellent Additives Which Prevent Moisture Transmission Between The Outer And Inner Leaf.