WARM AND AERO AND FITS LIKE A GLOVE. A lot of pieces in the Castelli line were designed for us to ride in. We love the Aero Race jersey so we wanted to have a thermal version for the fall and spring months.Featuring our Thermoflex Lite fabric its soft, warm, stretchy and highly breathable, yet with a tight weave that blocks out much of the wind. The back is in Warmer for enhanced breathability and to keep the pockets from sliding down. Its a race cut so that it really disappears when you have it on. Look and go as fast in the winter as you do in the summer.