Swimmers' tubes, also known as snorkels, are a type of breathing apparatus used by swimmers and divers. They consist of a tube that extends from the surface of the water to the swimmer's mouth, allowing them to breathe without having to come up for air. Snorkels are typically made of plastic or rubber and come in a variety of sizes and shapes. They are an essential piece of equipment for any swimmer or diver, allowing them to stay underwater for longer periods of time.