An alternative to the original Windstopper® Difesa cap, the Difesa Thermal is designed for less extreme winter conditions.
The Difesa Thermal loses the windproofing, but by doing so dramatically improve the moisture management, so it's best for cool to cold conditions, especially with high-intensity riding.
Castelli have used a rib-knit wool wrap around the ears to keep you warm but keep it all relatively thin to fit under a helmet.