These proprietary outerwear fabrics from Spyder are the result of years of research and development. OSMO fabrics are rated at 20k/30k, combining excellent waterproofing with an extremely high level of breathability which makes them great for aerobic activities in inclimate weather. The fabrics are part of a three-layer system, using an adhesive layer to bond a breathable laminate to the outer fabric. Based on the laws of osmosis, where it takes its name, OSMO fabrics are constructed in such a way that they allow water vapor to pass through to the outer layer of the jacket or pant, while preventing larger water molecules from breaching the laminate. One of the most breathable outerwear fabrics available.