The Arctic Series is designed for the high places that get really cold. This is the bag this is most often selected for expeditions to the northern mountains such as Mt. Denali and Mt. Logan and southern mountains such as Mt. Vinson. Even with a substantial differential cut between inner and outer fabrics, this bag will fit snug inside because of the amount of down pushing inwards. The XPD3 comes standard with waterproof-breathable Pertex Endurance shell fabric.