Let's cut to the chase: the Rab Expedition 1400 -40 Degree Down Sleeping Bag keeps you from freezing to death in the harshest environments on the planet. Period. Water-resistant Pertex Endurance and Microlight fabrics prevent outside moisture and body perspiration from compromising the loft of its 850-fill European goose down. This absurdly warm insulation traps precious body heat when you're sleeping 500-miles above the Arctic Circle or camped precariously above 20,000-feet. Also, the down's hydrophobic coating repels moisture from killing its heat-trapping loft. As if that's not enough, the massive amount of down filling amounts to over three-pounds in weight (fill weight is actually 49. 9-ounces) for a bag that's comfortable down to negative 40 degrees Fahrenheit. The warmest bag in the world isn't any good if your body heat seeps out the cracks like a leaky faucet. Realizing this, Rab carefully designed the Expedition with close-fitting neck and face baffles, complete with a collar and drawcord hood to lock-in fiery body heat in sub-zero temperatures. At the torso, the longitudinal baffles use Flowgate technology to keep down from migrating and subsequently leaving you with cold spots. The footbox has longitudinal baffles as well. Other well-thought features include an internal zippered stash pocket and dry bag compression sack for weatherproof storage and carrying.