A life vest is a flotation device you wear on your upper body to keep you from sinking in water. Also called a life jacket or personal flotation device (PFD), it's filled with foam or inflatable chambers that provide buoyancy, the upward force that makes things float.

Life vests are required safety equipment on boats, just like seat belts in cars. They're designed so that even if you're unconscious or too tired to swim, you'll stay at the surface with your head above water. Children wear brightly colored life vests at the beach or pool while learning to swim. Passengers on airplanes sit near life vests stored under their seats in case of a water emergency.

The vests work because they contain materials less dense than water, creating enough lift to support a person's weight. Modern life vests are much more comfortable than the bulky orange vests from decades ago. Some inflate automatically when they hit water, while others you inflate yourself by pulling a cord or blowing into a tube.

Whether you're kayaking down a river, sailing across a lake, or riding in a boat, wearing a life vest properly could save your life if you fall in. Even strong swimmers wear them, because accidents can happen in an instant.