This bag is a rare beast: It tested warm down to 15 degrees below its temperature rating. Our tester, wearing just a single layer of long johns, slept comfortably on a winter trip in Utah’s Bear River Range: “This bag puffs up like it has an internal compressor, and the 800-fill down with vertical baffles kept me in a constant bubble of warmth,” he says. “The hood surrounded my noggin in a cloud of down, and it cinched down tight without a bunch of extra material in my face.”
Despite all this warmth, the Mountain Light packs up to bread-loaf size. The fit is trim across the chest, but our 5’8”, 165-pound tester thought the increase in thermal efficiency was worth the tradeoff. The DWR-coated, 15-denier Pertex Quantum shell is both light and water-resistant. “I woke up covered in frost after an open bivy in Utah’s Cache National Forest, and no moisture penetrated the shell,” reports one tester.
The full-length zipper offers easy ventilation on warmer nights, and it ran smoothly every time, thanks to an effective snag guard (sometimes a challenging feature with these ultralight shell fabrics). $369; 2 lbs. 2 oz.; 15°F; ems.comGetting out in spring or pushing into fall, the Boreal, with warm PrimaLoft Infinity, packs small for use in all conditions.