The Seirus Heatwave Thick N Thin Headliner has an exclusive Heatwave thermodynamic lining with a 4-way stretch hood with cozy, 200wt technical fleece neck warmer. Thin Heatwave balaclava for kinetic&reflective dry, wicking warmth and a Polartec fleece neck-up for added warmth. Heatwave technology allows this headpiece to reflect the heat of your body, amplifying warmth and transforming a lightweight headliner into an amazingly warm piece of gear. With a thin skull and thick neck section, you get amazing warmth capacity out of a piece that also fits comfortably under helmets or hats. By combining the Heatwave material with 200wt performance fleece neck protection, the Heatwave Thick N Thin achieves maximum warmth with minimum bulk.