Let's get right to the point: the Rab Expedition 1400 -40 Degree Down Sleeping Bag is designed to keep you alive in the harshest environments on earth. Period. The water-resistant Pertex Endurance and Microlight fabrics are sandwiched around hydrophobic 850-fill European goose down, which has an absurdly high warmth-to-weight ratio, letting the Expedition check in at just over 4. 5lbs. It could be even lighter, but Rab designed it to be slightly roomier than usual, the better to accommodate the down clothing systems that can be essential during a high-alpine bivvy or penguin-freezingly cold arctic night. The warmest bag in the world is no good if all your body heat seeps out, so Rab was careful to design the Expedition with close-fitting neck and face baffles, along with a collar and drawcord hood, to lock the warmth in and the elements out. At the torso, the longitudinal baffles use Flowgate technology to keep the down from migrating and leaving you with cold spots, while the footbox features longitudinal baffles as well. There are thoughtful features, too, like an internal zippered stash pocket and anti-snag zipper tape to make your bag that much easier to use, and Rab included a drybag compression sack for easy and weatherproof packing.