Want to see a down bag puff up like a hot-air balloon? Unfurl one of these 850-fill sacks and stand back. Each bag in this line is overstuffed with the highest quality feathers we've seen–light, compressible, and amazingly lofty. And the down is well-distributed throughout–with enough on the bottom to keep your back from chilling if you roll over. The no-skimp approach to down has made these bags a tester favorite since 2001. Add Pertex Quantum shell fabric–which is breathable, wispy, water-resistant, and durable–and simple designs that are comfortable but thermally efficient, and you get standard-setting bags. If you require separate pockets for your iPod, make-up kit, and dental whitening strips, or other doodads like foot vents and pad straps, these elegant sacks are not for you. But what features there are we love: A muff around the face seals well without forcing you to crank down the drawstrings; the footbox is roomy enough for booties and hot-water bottles; and zippers stay zipped without relying on scratchy Velcro. Plus, there's a version for virtually every trip. Atom: $249, 40°F, 1 lb. 6 oz.; Hydrogen: $309, 30°F, 1 lb. 9 oz.; Helium: $359, 20°F, 2 lbs. 1 oz.; Helium EQ (waterproof/breathable): $429, 15°F, 2 lbs. 5 oz.; Lithium: $429, 0°F, 2 lbs. 12 oz.; (888) 357-3262; marmot.com.