The highest performing breathable Multifoil available Super FOIL SF40BB comprises 19 layers of top grade material carefully selected to create a breathable insulation that delivers optimum results. SF40BB provides a radiant barrier insulation & water resistant breathable membrane all in one & delivers a Thermal Resistance of up to 3.67 R value in a roof build. ideal to be used in Roofs & Walls in new build retrofit/renovations & extensions.