The Brooks-Range Mountaineering Hybrid Down Sweater gives you the warmth of a down sweater and the breathablity of Power Shield. The combination of 800 Fill goose down treated with DownteK and Polartec Power Shield create a warm down sweater that can be worn during aerobic activities. Brooks-Range used Power Shield in the back of the jacket to help breathability when you have pack on and on the lower part of the arms for durability. The chest and upper arms use a 20d Pertex fabric with 800 fill goose down that has been treated with DownTek. Because DownTek is water resistant it eliminate the possibility of external and internal moisture harming the loft of the down and losing warmth.