MIDWEIGHT BASE LAYER - The Hot Chillys Youth Micro-Elite Chamois Crewneck Thermal Shirt is the perfect thermal underlayer to keep kids warm, dry, and comfortable while skiing, snowboarding, or enjoying other outdoor activities; This thermal underwear top features a crew neckline with self binding and thumbholes to help keep sleeves in place MOISTURE TRANSFER FIBERS - The Hot Chillys base layers are designed for warmth, performance (including but not limited to breathability and moisture management), and wearable comfort; An essential feature in all Hot Chillys underwear is exclusive moisture transfer fibers (MTF) that move moisture away from the body by employing hydrophobic yarns to wick away perspiration, thereby keeping your child dry and comfortable BODY FIT AND UPF 30+ PROTECTION - Designed with 4-way stretch, this long sleeve undershirt for kids hugs the body for a next-to-skin fit, enhancing breathability and moisture management; Body fit garments move with your child, eliminating extra bulk and allowing a full range of motion while staying against the skin; In addition, this youth thermal underwear shirt has UPF 30 protection WARMTH FACTOR 8/10 - Ranked from Mild to Hot, the Warmth Factor Thermometer tells you how warm is Hot Chillys thermal clothing; Warmth Factors 6, 7, and 8 are considered Midweight and are very popular for most cold-weather activities; The Micro-Elite Chamois Crewneck long sleeve shirt for boys and girls has a warmth factor 8 out of 10, it features a smooth face for easy layering, and a soft fuzzy interior for extra warmth without adding bulk BIO-SILVER AND ACTIVATED CARBON - Bio-Silver ions have been intimately blended into some of Hot Chillys yarns to help your children stay fresh; In addition, activated carbon incorporated into the yarns enhance thermal regulation and smell-blocking characteristics of the Hot Chillys Micro-Elite Chamois Crewneck thermal underwear for kids