The hydration backpack included 2 Liter hydration bladder for men women kids. The perfect size offer a nice balance of reasonable weight and bulk while providing a sufficient quantity of water, fit for hiking, running, biking, climbing.The water backpack is lightweight, adjustable, comfortable. It made from breathable mesh back panel and high-quality nylon fabric, so that you will not feel sultry and uncomfortable during outdoor sports. It is the best choice for hiking, running, cycling, and climbing.