After years of watching a wide range of athletes buy its beloved Atmos road helmet for off-road racing, Giro decided to go ahead and design a mountain-ready version of the new Atmos II, and so created the Giro Fathom Helmet. A structural clone of the Atmos II, boasting the new Thermoformed SL Roll Cage, the Fathom gets its own styling and a removable visor, making it just that much more ready to hit the trail. The SL Roll Cage is the skeleton that gives form to the helmet's EPS liner. It keeps the helmet together under impact, acting like a second shell to maintain the helmet's structural integrity and disperse impact. The added strength also means that Giro can add negative space to the Atmos II without sacrificing safety, so it's more ventilated and lighter than its predecessor. The Atmos II still takes advantage of Giro's In-Mold Composite reinforcement, which permanently fuses the outer shell and SL Roll Cage to the EPS foam liner to enhance the effectiveness of all three. In an age of mass production, Giro's Roc Loc 5 Fit System makes the Atmos II fit like a custom one-off. You can custom tune the fit tension as well as the fore-aft tilt of the helmet in seconds with one hand. Though other helmet manufacturers have similar adjustability options, none of them even come close to the weight savings that the Roc Loc system offers; it's almost 40% lighter than comparable systems. Keeping your head cool during even the hottest, most critical road races is something that Giro has focused a great deal of attention on. Giro helmets are developed with a proprietary Wind Tunnel Ventilation System that combines 26 vents in the shell with exhaust channels within the belly of the helmet leading to the rear. Fresh, cool air from the front is strategically channeled around the head to help evaporate the sweat before exiting through the rear exhaust openings. It's a natural cooling system that you'll appreciate every ride.