We love eVent waterproof fabric for its superior breathability. We love premium 850-fill down for its awesome warmth-to-weight ratio. So we absolutely adore this bag, which teams those features via custom order. On trips from Mt. Whitney to Colorado's Elk Range, in temps as cold as the low teens, the eVent fabric boosted wind protection during open bivies and breathed well at subfreezing temperatures, where we've seen less breathable membranes lead to condensation (which compromises loft).
A waterproof flap over the zipper keeps tent drips and light showers from penetrating. The bag is a tad heavy given the price, but the performance of the shell fabric justifies the extra ounces. Bonus: Multiple lengths and custom girth alterations (for an additional charge) let you size Feathered Friends bags perfectly–a real plus for cold-weather campers. $524; 3 lbs. 2 oz.; 0°F Featheredfriends.com.