Marmot Never Summer MemBrain

First, bag-swapping testers were suspicious (“No way that’s warm enough—you take it”) and then greedy (“Never mind, I’ll pack the Plasma again today”). Who wouldn’t want to carry so little and sleep so warm? Whether in Alaska, the Adirondacks, or Capitol Reef, the response was unanimous: The cloudlike Plasma kept even cold-sleeping editors toasty on chilly nights that flirted with the bag’s temp rating (in both the 15°F and 30°F versions). The trick? Every detail is focused on efficiency.

The Insotect FlowGate system contours to your body, offering even insulation so none of the bag’s 900-fill down is wasted. Vertical baffles conceal smaller chambers spaced 10 to 15 inches apart; these cells help reduce cold spots by isolating the down and keeping it from shifting. And a 10-denier Pertex shell is 25 percent lighter than comparable shells; it’s so thin sunlight shines through, but we dragged the Plasma across slickrock like a toddler’s blankie with nary a lost feather.

And the shell enhances ultrafast drying: Four days of damp Denali trekking eventually soaked the footbox, but it dried with body heat after a few hours. A fat draft tube, snug collar, and deep, contoured hood seal the deal. Fit is narrow and efficiently trim, but not claustrophobic. (The zipper, however, required a little trial and error for a snag-free close.) Magic every morning: The 15 compresses down to volleyball size. Plasma 15: $469; 1 lb. 12 oz. (reg.); Plasma 30: $419; 1 lb. 6 oz. (reg.); two lengths; marmot.com