Is a device designed to assist a wearer, either conscious or unconscious, to keep afloat with his or her mouth and nose airway of his or her head's face above the water surface when in or on water. These devices from related ones, it is worthwhile to consider other types of devices.

Devices designed and approved by authorities for use by civilians recreational boaters, sailors, canoeists, kayakers differ from those designed for use by passengers and crew of aircraft helicopters, airplanes and of commercial vessels tugs, passenger ferries, cargo ships. Devices used by military air force, special forces, marines, navy, coast guard and police and enforcement agencies generally have features not found on civilian or commercial models, for example compatibility with other worn kit , survival vest, bullet proof vest body armor, equipment harness rappelling harness and use of ballistic nylon cloth to protect pressurized carbon dioxide CO2 canisters used for inflating the vest from injuring the wearer if struck by a round from a firearm. The ballistic cloth keeps the fragments from the canister from becoming shrapnel injurious to the user.

PFDs are available in different sizes and different designs purposed for various levels of protection.

The University of Victoria in British Columbia province Canada pioneered research and development into the Floater Coat patented UVic Thermo Float PFD which provides superior protection from cold water immersion immersion hypothermia through the incorporation of a neoprene rubber diaper that seals the user's upper thigh groin region from otherwise cold, flushing and debilitating water. Life jackets for outfitting large commercial transport in potentially dangerous waters, such as coastal cruises and offshore passages, and overwater air flights, are often a pair of twin or double sealed air chambers constructed of coated nylon sometimes with a protective outer encasing of heavier, tougher material such as vinyl, joined together but can also be constructed of foam aboard ships. Twin air chambers provide for redundancy in the event of one of the air chambers leaking, for example if the thin air cell fabric is sliced open by sharp metal fragments during emergency evacuation and egress.

Aircraft devices for crew and passengers are always inflatable since it may be necessary to swim down and away from a ditched or submerged aircraft: inflated or foam filled devices would significantly impede a person from swimming downward in order to escape a vehicle cabin. Upon surfacing, the person would then inflate the device, orally or by triggering the gas canister release mechanism.

Life Jackets always provide more buoyancy than buoyancy aids and the positioning of the buoyancy on the wearer's torso is such that a righting moment rotational force is developed that will eventually float most persons who are face down into a FACE UP attitude with their bodies inclined backward, unlike common foam buoyancy vests which are simply swimmers' aids, really since they don't generate re-righting moment forces. Self righting devices are be best for nonswimmers citation needed, who may not be able to orient themselves face up in the water, for example due to panic arising from finding themselves in deep, open water.

Today these air chamber vests are commonly referred to as Inflatable Life Jackets or Vests and are available not only for commercial applications but also for recreational boating, fishing, sailing, as well as kayaking and canoeing. They are available in a variety of styles and are generally more comfortable and less bulky than traditional foam vests.

The air chambers are always located over the breast, across the shoulders and encircling the back of the head. They may be inflated by either selfcontained carbon dioxide cartridges activated by the pulling of a cord, or blow tubes with a one way valve for inflation by exhalation. Some of the inflatable life jackets also react with the saltfresh water, inflating them. The latest generation of self triggering inflation devices, however, respond to water pressure when submerged and incorporate an actuator known as a hydrostatic release. Regardless of whether manually pull cord or automatically triggered, a pin punctures the cartridgecanister and the CO2 gas escapes into the sealed air chamber.

Drifting in open seas and international waters, as encountered by long sea voyages and military forces, require prolonged survival in water. The life jackets suited for this purpose are often attached to a vest with pockets and attachment points for distress signaling and survival, for example: a handheld two-way radio walkie talkie, emergency beacon 406 MHz frequency, signal mirror, sea marker dye, smoke or light signal flares, strobe light, first-aid supplies, concentrated nutritional items, water purification supplies, shark repellent, knife, pistol.

Offshore sailors and others can utilize accessories such as leg straps to keep the inflated chambers in position for floating in a stable attitude and splash or face shields constructed of clear seethrough vinyl which covers the head and face to ward off water from waves inundating the face nasal and mouth entries to the airway.