The castelli viva thermo skully cap is ideal for the colder seasons and has been made with a thermoflex material this cycling cap keeps heat on your head at the perfect temperature and its breathable properties ensure that you don39t overheat this castelli cap is cut to the geometry of your head to deliver a second skin feel and fits perfectly underneath your helmet without bunching the cap remains firmly in place throughout your ride and for a comfortable and effective thermal headwear t