When you’re in motion – climbing, hiking – regulating thermal comfort is essential. Made to balance air flow and insulation, the Proton Lightweight Vest wraps the core to deliver warmth without overheating. The Fortius™ Air 20 outer stretches and balances moderate wind and weather protection with airflow. Octa® Loft knit insulation provides warmth that resists packing out over time. The chest pocket and hand pockets provide secure storage, and the trim fit layers easily under a shell.