What Our Gearhead(R) Experts Are Saying:"I wear this under my helmet on every ride where the morning starts near freezing, and it never feels bulky or tight. Once the sun comes up and I've warmed into the ride, it's thin enough that I don't even think about it anymore."A cold head takes the fun out of an early start faster than almost anything else, and Castelli built the Pro Thermal 3 Skully to fix that without adding bulk under a helmet. We love how the soft, stretchy Thermoflex fabric hugs close to the head, trapping warmth right where a rider needs it most before the day has a chance to warm up.