A swim ring is a toroid

Toroid

Toroid may refer to*Toroid , a doughnut-like solid whose surface is a torus.*Toroidal inductors and transformers which have wire windings on circular ring shaped magnetic cores.*Vortex ring, a toroidal flow in fluid mechanics....

-shaped (hence the name "ring") inflatable

Inflatable

An inflatable is an object that can be inflated with a gas, usually with air, but hydrogen, helium and nitrogen are also used. One of several advantages of an inflatable is that it can be stored in a small space when not inflated, since inflatables depend on the presence of a gas to maintain their...

 water toy

Toy

A toy is any object that can be used for play. Toys are associated commonly with children and pets. Playing with toys is often thought to be an enjoyable means of training the young for life in human society. Different materials are used to make toys enjoyable and cuddly to both young and old...

.

The swim ring was derived from the inner tube, the inner, enclosed, inflatable part of older vehicle tire

Tire

A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...

s. The inner tube, when inflated, was used as a water toy, and as a floating object to lounge on.

A swim ring consists of two identically-sized layers of flat plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

, one of which contains a valve

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

. The shape of each layer is like a large circle

Circle

A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....

 with a smaller, concentric

Concentric

Concentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...

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, 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".

In America, swim rings are typically viewed as the toys of children and are generally only found in smaller sizes in childish designs. Other countries, however, attach no such significance and they can be found in many styles and sizes being utilized by all age ranges. Also, in America, it is becoming a fashion trend that is being used to help motivate overweight kids and as a fashion accessory. It is just starting out, but is received with good enthusiasm by kids and adults all over America.

Other swim ring designs include baby swim neck rings.

Besides named as "swim ring", it is also referred as "seoi pou" (water bubble in Cantonese) and "ukiwa" (float belt in Japanese);