Specially knitted to trap air for a soft and warm feel. 2.25 times warmer than our regular 'HEATTECH'. Based on CLO values, which measure clothing's thermal resistance. Comparison with standard 'HEATTECH'. Highperformance fabric with Heat Absorption, HEAT RETENTION, and moisturewicking comfort features. Ultra Stretch fabric. Soft texture and excellent shape retention. Brushed for warmth. Body width and sleeve length designed to wear like a longsleeved Tshirt or sweatshirt. Tshirt style collar is easy to layer.