Keeping our core primed is the key to sustaining energy on frosty morning starts, and Castelli's Perfetto RoS Vest offers engine-priming warmth. The front of the vest is designed to be windproof, while the back uses Castelli's breathable Nano Flex fabric to repel water. When the sun comes out to play and we start to warm up, the Perfotto RoS easily folds up and packs away in our cycling jersey pockets.