50m. Protect VP400 vapour permeable roofing underlay has excellent nail-tear and tensile strength while remaining lightweight and easy to cut. Used as an underlay for warm or cold roof construction, it helps to avoid the risk of roof-space condensation. Easily marked with a chalk line. 100% waterproof with unrestricted use in windy areas. UV and heat-resistant. BRE certified for all pitched roofs.