polyester Imported High Quality Material :Made from lightweight,breathable mesh back panel and high-quality nylon fabric ,that's very lightweigh comfortable and durable. Hydration bladder included: It's simple to drink, pull the rubber mouth piece out and the water comes right out. Push rubber mouth piece back to close, You don't have to bite anything! Our water bladders passed pneumatic pressure test, 24 hour swing test and 24 hour vibration test. It is completely pressure-tolerant and leak proof for carefree biking, running, hiking and other outdoor adventures! Adjustable straps:Adjustable shoulder straps,so you can make the backpack fit you perfectly and keep the pack from moving,Wide webbed shoulder straps help to reduce the burden of your shoulder. Two layers and reflective article design: one for the liquid container, and the other for keys, compass, phones, etc .Reflective article design for better safety. Perfect outdoor gear: If for any reason you are not 100% satisfied with Hydration Pack, please let us know and we will immediately refund your purchase price - no questions asked. KUYOU Hydration Backpack: Crafted for Runners, Cyclists and Hikers Designed for outdoor enthusiasts, the KUYOU Hydration Backpack combines lightweight durability with burden-free carrying. The 2L large-capacity water bladder meets all-day hydration needs for sports, while the bite-valve suction design allows one-handed water replenishment anytime. Reflective strips and a built-in survival whistle offer dual protection, keeping you safe from dawn to dusk.Whether tackling mountain trails or trekking through forests, KUYOU is your reliable sports companion.