Incredibly light and packable, the 850 fill power Cerium SL down vest weighs just 105 g (3.7oz) but provides exceptional warmth for its weight. Designed as a minimalist midlayer for cold, dry weather, its packability also makes it useful as a lightweight warming layer for autumn belays, evenings at camp and backcountry ski rest periods. Arc'teryx designers work tirelessly to uncover materials and develop designs that save weight while improving performance. The Cerium's 850 fill power goose down's warmth to weight ratio is outstanding. The unique, exceptionally light Arato 7 nylon shell is a highly compressible fine denier taffeta that provides remarkable durability and windproof properties. 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 intention and purpose. Down Composite Mapping technology is used to strategically place synthetic Coreloft insulation in areas prone to moisture. The internal pocket zips closed and includes a removable stuff sack. A simple elastic binding at the hem seals out drafts without the bulk of cordlocks, and the collar is carefully patterned to provide coverage while layering comfortably under a shell. A DWR treatment adds moisture protection.