Features Very strong and robust vapour permeable underlay. Water-proof Four- layer material. BBA, IAB and CE certified. Suitable for non ventilated cold and warm roof applications. No ventilation of the roof void required. UV Stable for four months. Hydrophobic treated.  Performance    Tensile Strength: BS2782-3.32OA. Longitudinal (N/5cm): 430. Transverse (N/5cm): 370. Nail Tear Strength: MOAT 27:5,4,1. Longitudinal (N): 364. Transverse (N): 392. Installation Permo Forte should be laid in accordance with our installation details set out in our Permo Product Guide and BBA Certificates.