The HydroSkin shirt is warm by itself on moderately cool days, and makes an ideal mid-weight addition between a thermal inner layer and a windproof outer shell. The Great addition to your gear bag.0.5-mm Terraprene keeps you insulated and stretches easily. ThermalPlush inner lining increases insulation, repels moisture and dries quickly.4-way stretch PowerSpan outer layer allows easy, unrestricted mobility. Lycra underarms eliminate binding, adding to this top's superior function either as a single outer layer or as a base layer. Titanium laminate adhesive aids in body heat retention. DWR coating forces H2O to "bead" and roll off the material.