Buyer: Use: breathable roofing underlay positioned immediately above the insulation layer in a warm pitched roof, or in a cold pitched roof (ventilated or unventilated). breathable roofing underlay for use under tiles and sheeted roofs, over open rafters or on to fully boarded substrates. breather membrane for timber frame wall construction. features: high performace breather membrane constructed from high tensile spun bonded polypropylene layers