Giro's ultralight helmet, the aptly named Prolight, weighs in at 22 grams less than the Aeon you see here. What do those 22 grams get you' A more adjustable helmet. The Aeon includes Giro's Roc Loc 5 adjustment around the circumference of your head, as well as strap buckles beneath your ears, neither of which you'll find on the Prolight. If you never wear a cap or winter hat, and the Prolight fits just fine, then you're 22 grams ahead -- for the rest of us, there's the Aeon.