The Pearl Izumi Thermal Skull Cap helps you to retain heat in frosty weather, with a full coverage design precisely tailored to fit under your helmet. P.R.O. Thermal Dry fabric provides quick-drying warmth, while reflective elements enhance low-light safety. The cap's mildly scalloped back prevents fabric bunching while in the cycling position, and an otherwise hidden rear port opens as needed to accommodate a ponytail.