In cool weather like freezing temperatures or snow, or when you’re travelling at highspeeds, your head can cool down quickly. You can prevent that with an insulatinghat or cap. They are as thin as possible so they don’t interfere under your helmet, which is good because helmets are generally made to provide plenty of ventilation.
When it’s really icy cold, you’ll benefit from a balaclava. These keep almost your entire face nice and warm. We also have lightercaps and hats that keep your ears nice and warm.