On the hottest days we need all the tricks we can get to feel comfortable on the bike: frozen cans pre-soaked hat frequent stops in the shade. Castelli's active cooling base layer adds to our arsenal of hot-weather technologies with innovative fabric allowing good temperature regulation in difficult conditions. Castelli uses Polartec's Delta knit fabric which combines hydrophilic and hydrophobic fibers for controlled drying and better evaporative cooling. Instead of the base layer drying immediately, it dries gradually so you can benefit from the evaporation of sweat and ride harder and further in hot weather.