The Arc'teryx CeriumThorium line enters the down jacket domain with an explosion a streamlined yet puffy explosion. The Men's Cerium LT Down Jacket is the lightest in the family at under a half pound, but it still packs a wallop of warmth. And actually, it's a hybrid in the family since Arc'teryx placed 850 fill goose down where it matters most your torso and arms, and then used synthetic Coreloft insulation in locations that are likely to suffer exposure to moisture, like the shoulders, collar, and along the hem. The dynamic duo of high tenacity Airetica face fabric and high warmth to weight down insulation fights cold on cloudless, bitter days. Wear this hybrid jacket over a thermal weight baselayer when you're hiking to find the perfect Christmas tree in the freak December cold snap, and wear it under a waterproof hardshell if you're skiing through a snowstorm. Whatever your pleasure, the Cerium jacket keeps you warm without being a burden, either on your back or in your pack. The trim silhouette means you can layer over the Cerium and still put your arms down comfortably by your sides. Underarm articulation gives you upper body mobility so you can plant a pole or chuck a snowball without tearing seams or exposing flank flesh. Arc'teryx designers made a name for themselves with their attention to detail, and the Cerium jacket illustrates their expertise. Light elastic cuffs won't pinch your wrists but will rebuke cold air attempting to slither up your arm. A chin guard on the collar prevents unattractive zipper rash caused when cold metal chafes against your chin. The included stuff sack makes it easy to pack this jacket when you're taking off for a week in the Winds and you need something warm for nighttime when the sun sets and crumbs from dinner have disappeared into the last gasps of embers.