Waterproof structure: hard shell construction with a sealed zipper mechanism that prevents rain and water intrusion, protecting internal contents from moisture in challenging environments. Flexible portability solutions: adjustable shoulder straps and hand rings support multiple carrying methods, including handheld or singleshoulder use, ensuring the rear bike rack bag remains practical and userfriendly in diverse situations. Improved road visibility: embedded brightness reflective strips reflect light effectively at night or in lowlight environments, boosting rider visibility and road safety during rides. Useful and functional storage: main compartment accommodates water cups, tools, clothing, and more, keeping cycling essentials organized; a front interlayer provides dedicated space for keys, cards, and small items. The 8.6L threedimensional structure offers optimized storage for convenient access during rides. Designed for rear rack mounting: specifically built to install on rear bike racks, ensuring secure attachment and dependable performance on a variety of bikes and setups. Use scenarios: City commuting: carry a water bottle, tools, and a light jacket in the main compartment, with keys and cards kept in the front interlayer for quick access at stops. Weekend rides or errands: ample 8.6L capacity supports your daily gear, snacks, and extra layers, while adjustable straps allow easy handheld or singleshoulder carrying off the bike when needed. Rainy or lowvisibility conditions: waterproof shell keeps contents dry, and reflective strips enhance visibility to motorists and other road users during night or poor weather rides.