4-Way Stretch Moisture Control/Breathable Heatwave℠with Integrated Spandex for Improved Stretch, Shape, and Maximum Comfort †Ergonomically Placed Max Wick℠Fabric For Increased Breathability †High-Performance Power Mesh for Increased Breathablilty at Perspiration Zones A thin base layer with ultimate warmth - the Heatwave℠reversible top harnesses the amazing warming power of Seirus exclusive Heatwave℠technology. The heat-reflective material amplifies 4-5 degrees while also reflecting 20% of your escaping body heat back to you. With brushed Max Wick℠next to skin for optimal wicking and ventilation throughout. By maintaining a warm core you increase blood flow, which also helps keep your extremities warm.