General: inner tube
A flotation device used as a swimming aid, especially by young children and older persons who cannot swim. So called because it resembles (and in early times, probably was) the inner tube of a car tire. Currently made most of PVC.
Often constructed of transparent material, ostensibly for better visibility of the wearer.
A lifebuoy is visually similar, but its use and usual material composition are different.
The following are aliased to this tag: innertube