Stay warm and protected in extreme cold with Men's 'HEATTECH' Ultra Warm T-Shirt, UNIQLO's most advanced thermal base layer designed for maximum insulation and comfort. Powered by cutting-edge 'HEATTECH' technology, this ultra-warm T-shirt captures body moisture and converts it into heat, delivering superior warmth without added bulk. The soft, stretchable fabric ensures a snug fit that moves with you, while moisture-wicking properties keep you dry and fresh all day. Whether layered under outerwear or worn solo, this thermal essential is perfect for winter commutes, outdoor adventures, or cozy indoor wear.- 'HEATTECH' Ultra Warm Technology: Generates and retains heat for enhanced thermal insulation.- Ultra-Warm Fabric: Provides maximum warmth while remaining lightweight.- Soft and Stretchable Material: Offers a comfortable fit that moves with you.- Moisture-Wicking Properties: Keeps you dry by drawing sweat away from the skin.- Lightweight Design: Ideal for layering or wearing on its own in cold weather.-Essential Thermal Base Layer: Perfect for winter sports, travel, or everyday cold-weather outfits.Compare 3 Types of 'HEATTECH' Fabric:'HEATTECH'- Lightweight yet warm, ideal for everyday layering. - Recommended for 41 °F to 68 °F for mild winter days or cozy indoor wear. 'HEATTECH' Extra Warm- About 1.5× warmer than original 'HEATTECH', offering added insulation without bulk. - Perfect for colder days with recommended temperatures from 23 °F to 59 °F. 'HEATTECH' Ultra Warm - Our warmest option, approximately 2.25× warmer than original 'HEATTECH'. - Designed for more extreme cold with a recommended range of -4 °F to 50 °F. Men's HEATTECH Ultra Warm T-Shirt with Moisture-Wicking Navy XS UNIQLO US