- The ultimate thermal base layer, even in the most extreme cold. - Ultra Warm is 2.25 times* warmer than our regular HEATTECH. *Based on CLO values, which measure clothing's thermal resistance. Comparison with standard 'HEATTECH'. - High-performance fabric with Heat Absorption, HEAT RETENTION, and moisture-wicking comfort features. - A warm layer with a fluffy, brushed lining. - Stretch fabric allows easy movement even when layered. - Flat knit creates a neat, clean impression. - Simple crew neck design. 41% Acrylic, 37% Polyester, 18% Rayon, 4% Spandex