As light and compressible as functionally possible, the Cerium SL down vest weighs a scant 120g (4.2 oz) but delivers exceptional warmth for its weight. A minimalist midlayer for cold, dry situations, its lightweight packability also makes it useful as a warming layer for autumn belays, evenings at camp and spring backcountry ski rest periods. The 850 fill power goose down's warmth to weight ratio is outstanding. The Arato 7 nylon shell is a highly compressible fine denier taffeta that provides remarkable durability and windproof properties for exceptionally little weight. Because the Cerium SL is intended as a midlayer, Arc'teryx is able to use sewn through construction to further reduce weight and increase packability. True to detail, the Cerium's zippers are minimized to reduce weight and bulk. Features and construction reflect disciplined, purpose driven design. Down Composite Mapping technology is used to strategically place synthetic Coreloft insulation in areas prone to moisture. The single chest pocket includes a removable stuff sack, elastic at the hem seals out drafts, and the collar is carefully patterned to provide coverage while layering comfortably under a shell. A DWR treatment repels light precipitation.