The DrymaxX membrane itself breathes, i.e. lets air molecules through. As a whole, the upper materials and fillers affect the breathability of the shoe. The DrymaxX membrane works on the principle of osmosis and is usually combined with a moisture-wicking textile lining. However, choosing the wrong sock can destroy the membrane's functionality; cotton and wool, for example, are fibers so absorbent that they do not allow moisture to evaporate, but absorb all the moisture into themselves, resulting in wet and cold feet.