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A swim ring (also known as a swim tube, rubber ring, water donut, or, in the United States, a lifesaver) is a toroid-shaped (hence the name "ring" or "doughnut") inflatable water toy. The swim ring was derived from the inner tube, the inner, enclosed, inflatable part of older vehicle tires. The inner tube, when inflated, was used as a water toy, and as a floating object to lounge on.
The swim ring is not designed to save individuals from drowning.
A swim ring consists of two identically-sized layers of flat plastic, one of which contains a valve. The shape of each layer is like a large circle with a smaller, concentric circle removed. The two layers are joined at their inner and outer edges, sealing an air chamber inside.
Swim rings (also called "swimming rings", "swimrings", "inner tubes", "innertubes", "rubber rings" or "floaty/floaties") are inflated with air and worn around the user's torso, usually just under the arms or sat upon, to hold the user above the water. They come in a variety of sizes to fit children through adults, though the larger sizes are often called "swim tubes" or just "tubes". There are also variant forms of tubes like boat and fish available. Other swim ring designs include baby swim neck rings.
At water parks, these are commonly used on water slides, with a person sitting in the center of the ring, legs and body leaning over the sides. Some designs even appear as more than one tube sewn together, and include 2 or 4 holes so that more than one rider can fit comfortably.