Leveraging the lightweight performance of Coreloft synthetic insulation, Airetica ripstop nylon and highly efficient ergonomic patterning, Arc'teryx created a hooded alpinist's belay jacket that packs to the size of a water bottle and delivers effective warmth for a mere 285 grams. Articulated patterning and underarm gussets provide elevated ergonomic freedom. The fit is trim for maximum thermal efficiency. Utilizing different volumes of Coreloft insulation helped Arc'teryx reduce weight and bulk without sacrificing effective warmth. Using a mapping for warmth approach, they placed loftier 80g Coreloft in the body, and a 60g Coreloft in the sleeves and side panels to aid breathability, reduce bulk and add mobility. The Nuclei's internal pocket serves as an integrated stuff sack. A carabiner clip loop makes it easy to fasten to a harness or pack. Elastic binding around the sleeve cuffs and hood are light, smooth and create a secure fit. Hand pockets have streamlined, invisible zippers.