Get ready for your daily commute or next weekend ride with our versatile rear rack bike bag. This expandable carrier easily transitions from a compact 13 L pack to a spacious 18 L double pannier setup, making it simple for everyone to pack their gear. Premium features like splash-resistant 300-denier (300D) polyester with a polyethylene (PE) foam interlayer, two expanding side pockets, and high-visibility reflective elements. Featuring four strong hook-and-loop straps for a quick, secure mount on your bike and a convenient shoulder strap for comfortable off-bike carrying. FEATURES: Spacious zippered main compartment, internal mesh pocket, rear water bottle holder (bottle NOT included), and 2 zippered side pockets keep all your gear, daily essentials, and bike tools organized and accessible on the go. Side pockets expand to full panniers, increasing the bag’s capacity from 13 L to 18 L. (Note: The expanded capacity is approximate.) Integrated water bottle holder with an elastic drawstring and cord lock firmly holds your bottle. Tightly woven 300D polyester fabric with PE foam interlayer resists splashes to help keep your belongings dry. Includes built-in carry handles and a removable, adjustable shoulder strap for comfortable, easy carrying when off your bike. 4 strong hook-and-loop straps hold it securely to rear racks less than 10.2 inches in width. Reflective elements on the sides and a back reflective tab with taillight mounting loops (taillight NOT included) provide enhanced nighttime visibility. Perfect for trips on roads or trails.