The front panel is constructed using our NEOS Medium, which is a 3L softshell with PU bonded membrane. Highly breathable, waterproof, insulating, and 100% windproof, this flexible house-developed textile ensures your core stays fully protected. The tops of the arms and upper back are made with NEOS Light, which scales back insulation in favor of boosted breathability and lower weight. And to keep you from overheating as your effort levels rise, the underarms and back use our fleece-backed RX material.