Petzl - ALVEO VENT, Ventilated Helmet for Rescue Work PROTECT YOUR HEAD: Impacts are absorbed by deformation of the expanded polystyrene liner. STAYS PUT: Strong chin strap (more than 50 daN) limits the risk of losing the helmet during a fall. COMFORT IS KEY: CenterFit adjustment system adjusts the headband and keeps the helmet centered on the head. BREATHE EASY: Features ventilation holes that allow airflow through the helmet. PERFECT FIT: The ALVEO VENT comes with two sizes of headband foam.