The Marmot CWM MemBrain -40 Degree Down Sleeping Bag is for the extreme bag for the worst conditions. High in the Himalayas, No Problem. Deep in the Andes, No Problem. Deep in the Alaskan backcountry, No Problem. This is possibly the warmest,best sleeping bag in the world. High-quality 800+ fill-power goose down and Pertex Shield waterproof, breathable fabric form the core of this portable environment designed to deliver restful sleep in the harshest alpine environments. Over-engineered with sturdy reinforced linings and countless baffles for a lifetime of dependable comfort and protection.