ISOFOIL expanded polystyrene insulation with reflective aluminum vapour barrier. Provides superior performance. Designed to insulate interior of foundation walls. The reflective effect of the vapour barrier transfers emitted heat through energy sources such as lighting. Vapour barrier function reduces the risk of condensation by preventing humidity from passing through insulation and contacting cold concrete, thus preventing mould and mildew. Thermal resistance of R-15.5*. L-rabbeted on both 8-ft sides. *R-15.5 attained with installation of 1 in. x 3 in. slats.