A traditionally shaped cycling cap but with extra warmth and water protection from Castelli's Nano Flex 3G fabric. It fits comfortably under a helmet with minimal bulk but adds significant warmth for cold rides. This cap provides a high degree of warmth, especially in temperatures close to freezing and for riders who tend to sweat a lot and need the breathability of Nano Flex. If you're riding in extremely cold conditions, then look to the Estremo WS Cap.