No matter what the season, some prefer to go it alone in the mountains. And for minimalists of that mindset, MSR created the all-weather AC Bivy and outfitted it with a waterproof breathable top and a DuraShield-coated floor. Top and bottom protection from rain, sleet, snow, and wind is vital, but all is lost if you sweat to death during the first five minutes inside. To this end, the AC uses a zippered mesh closure that helps to vent some of that hot air out and away. Slide your sleeping bag inside this simple one-pound sack, and stay dry while you sleep off a long day of pounding trail or pulling rock.