REI Co-op Trail Hydro 20L Review | Tested & Rated。EUC REI Co-Op Trail Hydro 30 Backpack * Capacity 30 liters * It is designed to accommodate a hydration reservoir with a specific internal sleeve, bladder not included. * Features a top zippered pocket, side mesh pockets for bottles, and hip-belt pockets for easy access to small items. * Main body is ripstop nylon with durable water repellent finish * Includes padded, mesh covered shoulder straps and a back panel designed for comfort and ventilation * Excellent used condition - could be mistaken as new * Color grey