The Big Agnes Mystic Sleeping Bag is filled with light, compressible 850 fill DownTek waterproof down and weighs only 2 lb 5 oz. Like all Big Agnes sleeping bags, the Mystic has an integrated pad sleeve so you never roll off your pad again. Removing the insulation on the bottom also reduces weight since compressed down has no insulating effect. The Mystic is an upgraded version of the popular Big Agnes Lost Ranger Sleeping Bag.Flow Construction: Insotect Flow is a flow optimized insulation system that delivers uniform heat distribution and natural body contouring through its revolutionary baffle design. Flow Construction eliminates lateral and vertical down shifting by using vertical chambers with Flow Gates to regulate fill positioning and density. Strategically placed Flow Gates minimize vertical down shifting while vertical chambers minimize lateral shifting. With continuous vertical Flow chambers in place of traditional side seams, Flow bags eliminate potential cold spots which can occur with side seams. Vertical baffles now flow with your body for more rapid and uniform body heat distribution.