Mardingtop Running Backpack Ultralight Hydration Pack for Trail Water Walking Hiking Bicycle Cycling Running Climbing MATERIAL- Polyester.These water-resistant fabrics do not allow water to easily penetrate. Breathable mesh shoulder straps and mesh back panel.Keep your back and shoulders cool and comfortable. FEATURES- Adjustable abdomen strap and sternum strap for perfect placement and bounce free ride. Sternum strap with emergency whistle buckle. HYDRATION SYSTEM COMPATIBLE- External hydration bladder's compartment and open type water tube outlet. Big enough for 2 liters hydration bladder. (Hydration Bladder is not included). ZIPPER POCKETS- allow easy access to your key,camera,phone,wallet etc. Both side of the shoulder strap has an elastic pouch for small item like powerbar,GPS,phone or water bottle. VERSATILE- Ultra-light Running Backpack for Men, Women, Teens, Kids. Perfect for Walking,Cycling,Hiking,Travel,Climbing,Running Race,Jogging or other sports.