An ultra-light, cooling, sleeveless baselayer that provides warm weather comfort. An ultralight, cooling, sleeveless baselayer that provides warm weather comfort. Secretly cool Secretly cool Even warmer rides can benefit from the right baselayer. Bontrager's lightest weight baselayer fabric, B1, is a comfortable first layer of Profila Cool fabric enhanced with 37.5 technology that regulates the body’s relative humidity to maintain ideal core temperature, allowing greater on-bike performance. Comfortably fits under every jersey you own. Even warmer rides can benefit from the right baselayer. Bontrager's lightest weight baselayer fabric, B1, is a comfortable first layer of Profila Cool fabric enhanced with 37.5 technology that regulates the body’s relative humidity to maintain ideal core temperature, - Profila Cool fabric powered by 37.5 active particle technology Profila Cool fabric powe...