Engineered for climbing and mountaineering, Petzl's Ecrin Roc Helmet offers an array of side vents in the polycarbonate shell that can be plugged (plugs sold separately) for thermal comfort in icy winter conditions. The headband adjustment is so versatile that the helmet easily accommodates head circumferences ranging from 21 to 25 inches. Two foam headbands are included so you'll have no problem tailoring the Ecrin Roc for a perfect fit.