The Aeon Helmet has quickly become a favorite of the pro peloton with a unique design that manages to combine the best features with incredible ventilation, easy fit adjustment and an impressive 218 gram weight. All giving you Pro Tour level helmet that will give you an advantage when the road climbs and the heat turns up. This helmet is feathery light at 218 grams size medium due to Giro's extensive research and development. Amazingly... though, it passes the CPSC testing just fine for safety standard for impact resistance. It comes with Giro's all new Roc Loc 5 retention system. For starters, the indexed Micro Dial lets you adjust the tension with a two fingered twist. And its three position bracket allows 15mm of vertical adjustment in the retention basket enough to fit any head shape comfortably. The Aeon uses in mold construction to fuse the foam liner to the abrasion and puncture resistant polycarbonate shell as other Giro helmets. However, Giro uses a low density EPS liner for the Aeon that performs the same important task of absorbing impacts. A thermo formed SL Roll Cage reinforces the Aeon for maximum safety, yet it's 49% lighter than the Ionos' composite sub frame.C23 The Giro Aeon Helmet has 24 massive Wind Tunnel vents to suck cool air in the front and flush warm air out the back, even at relatively slow speeds.