Permo® air is the most breathable air open low resistance underlay on the market. It is the ideal solution where there is a high risk of condensation forming in the roof space. Features Air open & vapour permeable. Over 13% more breathable than any other ‘air open’ underlay on the market. Lowest vapour resistance of all breathable membranes. Being both air open & vapour permeable further minimises the risk of condensation forming, particularly during the drying out period of a building. No ventilation required. Hydrophobically treated. Type LR underlay. Strong 3 layer material. 15 year guarantee. Recyclable. UV stable for 4 months. Batten spacing 350mm. Superior nail tear strength. Suitable Cold and warm roof applications. Please note no ventilation is required with this product.