This pack keeps anywhere from 2-4 water bottles secured to your chest while you run. The bottles can be centered and adjusted for balance, and they are easy to reach and holster. The vest may be more lightweight than a backpack hydration system, or a belt with multiple bottles on it. Your water is kept where the body makes the least amount of movement while running. This means no annoying sloshing sounds that you might normally hear from carrying your water in your hand. These vests are typically made out of nylon and mesh, so they are easy to clean and last a long time.