The Pro Thermal headband is thin but warm thanks to Castelli's lightweight Thermoflex fabric. It is more than wide enough to cover the ears and easily fits under a helmet. Remember headbands allow for heat to escape from the top of your head, something caps will not due. This will cut down on unnecessary perspiration which is the kiss of death on colder rides. The Pro Thermal is perfect for those who like warmth without the bulk and is considered by many cyclists as the best 3 season headband, as it is ideal for cool mornings in the mountains in June and September.