Mammut's lightest and most packable insulated jacket, the Aenergy IN Hooded Jacket is just what backcountry skiers, mountaineering, and winter hikers need to crush our winter activities. The Aenergy features hydrophobic, 850-fill power down—that's not only as light and lofty as it gets but also insulates in wet conditions (unlike untreated down). We like this hoodie as an outer layer or ultra-warm mid-layer, and we like how small it packs down into its own hand pocket.