Using Seirus exclusive modern fibers the Dynamax Skull Liner provides awesome warmth, wicking, and wind block in a thin, lightweight package. With Dynamax, the feel is unreal. Seirus' exclusive dual-density, micro denier hollow-core Thermax material is warm enough to wear alone, but thin enough to layer under hats, helmets, or anything else. Recommended for: On-mountain cold weather adventures (skiing, snowboarding, hiking, fishing, etc), activities in high wind | Seirus Dynamax Skull Liner Hat