Water bags, sometimes referred to as hydro or aqua bags, function nearly the same as heavy bags and come in a number of shapes and sizes. They are typically made of a durable, but thick, soft plastic and filled with water. One notable difference is that water bags can be shaped like short teardrops. This is helpful for training uppercuts, a skill not accurately trained on traditional heavy bags. Another advantage water bags offer is the ability to perform long, intense combinations. This is thanks to the better shock absorption that the water filling offers. Additionally, boxers will often prefer water bags over heavy bags because of their reduced risk of injury.