- Waterproof and durable: the bag uses carbon fiber grain leather with a waterproof TPU coating on the surface and interior. Built-in PP board provides rigidity, helping the bag keep its shape while protecting contents from rain and light impacts. - Easy installation and removal: attaches under the bicycle frame tube with an adjustable Velcro strap. The Velcro fastener is made of non-slip, soft leather to reduce friction on the inner tube. - Optimized storage for small items: ideal for smartphones, wallets, keys, small bike pumps, cable locks, repair tools, and other essentials. Main compartment sizes: M is 9.3 inches x 2.6 inches x 4.1 inches; S is 8.5 inches x 2.2 inches x 3.3 inches. - Easy open design: features a large zipper for quick, convenient access to stored items. - Practical use scenarios: - Daily commute: keep your phone, keys, and wallet secure and dry without adding bulk. - Short rides and errands: store a mini pump, multi-tool, and lock within easy reach. - Light bike touring: lightweight storage for essential tools and small accessories while maintaining a tidy frame.