We would have no problem asserting that the Castelli Viva Thermo Skully is the perfect cool weather cycling cap. The ThermoFlex material that comprises it is warm and soft, stretching easily to accommodate a wide variety of domes, yet it’s also especially breathable and never lets you overheat. It’s raw-cut edges don’t bunch and won’t apply pressure points to your head under your helmet, making this light cap something you’ll almost forget it’s there — until you take it off, of course.