Cavity Wall Insulation (CWI)

Insulation material - commonly mineral fibre, EPS (expanded polystyrene) beads, or blown foam - injected or blown into the air cavity of an existing cavity wall to improve thermal performance. CWI is one of the most cost-effective energy efficiency improvements for post-1920s homes. New-build extensions incorporate rigid or semi-rigid cavity board insulation installed as the walls are built.