The Mist Hydration Backpack has an elastic sport mesh helmet harness. The Mist Hydration Backpack is compatible with most 2L hydration reservoirs, helmet, most 15" laptops, and then some. The zippered sunglasses compartment in the front keeps your shades in the same protected place, while the front pocket organizer keeps your cell phone, wallet, keys, and other small items in their assigned places. This bag comes complete with side compression straps to stabilize your load, a buckle on the shoulder straps to keep your pack in place while you're moving, and a padded cooling back channel to keep you cool and comfy. The elastic helmet carrier stows away while you're not using it so you're more aerodynamic while you ride.