Skull caps split into two categories: thin ones that barely register under your helmet, and thermal versions that turn your head into a sweat lodge the moment you start climbing. The Pro Thermal 2 Skully from Castelli lands in the thermal camp but manages the heat buildup problem that makes most winter caps unwearable once your effort level rises. The secret is Castelli's approach to fabric weight and breathability—enough insulation for genuine cold weather protection without the suffocating feel that forces you to strip the cap off mid-ride.

The construction uses Castelli's Thermoflex fabric across the main body, which provides the wind protection and warmth you need when temperatures drop into the thirties and below. An integrated panel across the forehead adds structure without creating pressure points under your helmet straps, and the fit sits close enough to your head that there's no bunching or shifting once you're clipped in and moving. The ear coverage extends low enough to actually protect your ears—something cheaper skull caps often miss by cutting the pattern too short in the name of a cleaner look.

Where this cap earns its keep is on those rides that start in genuine cold and end with you working hard enough that heat management becomes the priority. The Thermoflex fabric breathes better than solid fleece alternatives, which means moisture moves away from your scalp instead of pooling under your helmet. If you've ever finished a winter ride with a soaking wet head despite sub-freezing temperatures, you understand why this matters. The Pro Thermal 2 Skully works best in the twenty-to-forty-degree range where you need real thermal protection but your body is still generating significant heat.... Read More