"DWR (Durable Water Repellent):A DWR-treated fabric will bead-up water on its surface to stop it from soaking into the fibres. This maintains breathability and shortens drying times. Waterproof Rating:This is measured and expressed as Hydrostatic Head in millimetres (mm). To find out the Hydrostatic Head of a fabric the manufacturer will take a clear tube and clamp their material over the bottom end. They will then fill the tube slowly with water and watch to see how high the column of water can get before the material lets drips through. The higher the hydrostatic head, the better the water protection. The European Standard a fabric must meet to be classified as waterproof is a Hydrostatic Head rating of 1500mm, and on average, outerwear fabrics tend to have a hydrostatic head of 10000mm and above. Breathability Rating:Breathability is measured as a rating in grams of how much vapour a square metre of fabric will allow to pass through in 24 hours (g/m2/24). For general use, 10000g/m2/24 and above is desirable. It should be noted that breathable fabrics do not stop you sweating and care should be taken as to clothing worn beneath waterproof/breathable shells. High quality base layers and fleece or insulated midlayers should in themselves draw vapour from the body and pass it outwards, thus allowing the outer fabric to do its job. Cotton clothing should never be worn as part of a performance clothing layering system."