Castelli Active Cooling Sleeveless Base LayerWearing multiple layers when you're trying to stay cool may sound counter-intuitive, that is before you knew Castelli designed the base layer and integrated their performance technology into the fabric. Introducing the Castelli Active Cooling Sleeveless Base Layer, essentially a tank top you wear under your jersey that is designed to be super-breathable and keep your core cool. The secret to the active cooling is Castelli's PolartecA(R) Delta fabric, a combination of hydrophilic and hydrophobic yarns which absorb and repel sweat, simultaneously holding the moisture close to your body and helping to evaporate it. This base layer is meant to be worn under a breathable jersey.FeaturesPolartecA(R) Delta fabric Features regulated drying so that the evaporative effect cools your core.Minimalist construction Sleeveless base layer.Lightweight 84 grams.SPECIFICATIONSMaterialPolartecA(R) Delta fabricSleeve LengthSleevelessClosure TypeNoneFitBase layer, fittedIntended UseRoad, XC, TrailSpecial FeaturesPolartecA(R) Delta fabricSizing (Inches)SizeExtra smallSmallMediumLargeExtra Large2X LargeChestLess than 363637.5394143WaistLess than 31313334.536.538.5 | Castelli Active Cooling Sleeveless Base Layer Men's Size Extra Small in Silver Grey