For those situations when you need some insulation during your belay shift, but not enough to haul out the full-on insulation. A combination of 80g Coreloft throughout the core keeps you warm; 60g in the sleeves and side panels keeps you trim and mobile. Trim fit makes the Nuclei feel as comfortable as a sweater, except better. Nothing gets in your way, nothing snags or flaps around the cuffs. The trim fit keeps you lean, clean and holds the warmth close. Compresses into the interior pocket and has a clip in point for fastening it to your harness. Elastic binding around the sleeve cuffs and hood are light, smooth and keep a secure fit. Hand pockets have streamlined, invisible zippers.