This product comes into the Castelli lineup as a direct request from Timothy O’Donnell when he wanted to do better than his fifth place Kona finish. The objective is clear: keep cool and comfortable during the run. We took our insanely light and ventilated A-Vent fabric and gave it a loosish cut to allow maximum airflow between the top and the body. The top weighs next to nothing but covers a wide range of conditions: the fabric is excellent at keeping you dry when you want it too but really shines when you need cooling and can pour water over it at the aid stations.