When it;'s not horribly cold, but you need and prefer a brimmed cycling cap with warmth and water protection, along with reasonable breathability, Castelli has you covered. The Pro Nano Thermal Cap is 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. Most riders can anticipate comfort from 32-55°F with this great piece from Castelli.