100% Polyester Imported ACTIVE FIT AND UPF 40+ - Designed to follow the lines of the body, usually with some amount of stretch fabric. These garments have a lighter feeling fit, with less bulk than a relaxed fit thermal base layer. They are especially perfect for year round, multipurpose use under layers. Ultraviolet Protection Factor. Sunlight includes rays of ultraviolet (UV) radiation, and Hot Chillys products are designed to help protect you! MECHANICAL STRETCH. Engineered to stretch and move with you, providing all over fit, warmth and expedited moisture movement. WARMTH FACTOR 10/10 - Ranked from Mild to Hot, the Warmth Factor Thermometer tells you how warm each of our products is. Warmth Factors 6, 7, and 8 are considered Midweight and are very popular for most cold-weather activities. MOISTURE TRANSFER FIBERS - An essential feature in all our products, Hot Chillys exclusive moisture transfer fibers (MTF) move moisture away from your body by employing hydrophobic yarns to wick away perspiration, thereby keeping you dry and comfortable. ODOR-BLOCKING PROPERTIES - Fabrics that feature the OBP label have been specially treated with our secret “chilly seasonings”. These products are designed for optimum freshness and will remain in the fabric for the first 20-30 wash cycles.