Now you can enjoy Birkenstocks in winter too with the Womens Boston Sheepskin lined mule. The upper is made of premium quality light grey suede leather and the footbed is lined with super soft shearling - a neatly trimmed sheepskin. Sheepskin helps with temperature regulation ensuring your feet arent too hot or too cold and benefits from being biodegradable Birkenstock - Boston Fur Sheepskin 1017650-03 (light Grey Suede)