Superfoil SF19BB Breathable Insulation 1.5m x 10m Roll 15.0 m2 Reflective Breather Membrane & Thermal Insulation Combined For Roofs & Walls. Watertight W1 & Breathable 40mm Thickness For technical details please refer to the PDF data sheet which we link to below in the "Additional Information" notes. Product normally requires a minimum of 25mm air gap either side of the multi-foil to ensure that this product works in the way that it was designed to.