||This article needs additional citations for verification. (March 2012)|
A lifejacket is a type of personal flotation device designed to keep a person's airway clear of the water whether the wearer is conscious or unconscious. They are either made from two layers of bonded polyurethane to be inflated or from foam.
The inflatable lifejacket is probably the most widely used for both leisure and commercial activities, while the foam lifejacket is predominantly designed either for children, or for emergency use (such as on ferries, cruise ships etc.).
Types of inflation 
There are four inflation methods for air-only lifejackets. It is important to know which method your lifejacket uses and how it works.
Oral Some older lifejackets had oral inflation as their only method of inflation, normally via a one-way valve. Although intended for oral inflation, a suitable low pressure pump may be used if preferred. These lifejackets should be fully inflated before going afloat, and should be worn fully inflated until the wearer is back ashore. Although it is doubtful whether these are still in production, they may still be found in use. Modern lifejackets, inflated by means of a gas cartridge, usually if not always have oral inflation as well; this is intended for topping up if the casualty is in the water for an extended period while awaiting rescue, but may also be useful for inflating the lifejacket for test purposes to verify the integrity of the bladder.
Manual Manually inflated lifejackets are operated by pulling a string, which pushes a firing pin into the CO2 canister, inflating the lifejacket. Automatic and hydrostatic lifejackets both have a manual pull string as back up.
Automatic Automatically inflated lifejackets rely on a small pellet or bobbin, which holds back a powerful spring. When the pellet makes contact with water it dissolves very rapidly, releasing the spring, which pushes a firing pin into the gas canister.
Hydrostatic (Hammar) Hydrostatic or Hammar action lifejackets work the same way, but the pellet is protected by a case that only lets water in once it is a few centimetres below the surface. It won’t fire until fully submerged.
Choosing a child's lifejacket 
All children’s lifejackets state a maximum weight and chest size that must not be exceeded. It is equally important not to buy a lifejacket that is too large, as this may result in the child slipping out of it or the lifejacket floating high in the water leaving the child’s mouth and nose submerged. A good way to tell if a lifejacket is the right size is to fit and adjust it and then lift it from the top. It should not be possible to lift the lifejacket more than 2.5 cm from the child’s shoulders.
Lifejacket requirements for children in the United States 
In the United States, lifejackets are generally required for children; however, the age range varies in different states.
Choosing an adult's lifejacket 
The BoatUS organization (Boat Owners Association of The United States) tests lifejackets of various types, and publicizes its results. (More information on choosing adult and children's lifejackets in the External links section below).
Lifejacket types in the UK 
The 100N lifejacket 
The 100N lifejacket is for those who may have to wait for rescue but are likely to be in sheltered, calm water. It may not have sufficient buoyancy to protect someone who is unable to help himself or herself and may not roll an unconscious person on to his or her back, particularly someone in heavy clothing.
The 150N lifejacket 
The 150N lifejacket is for general use on coastal and inshore waters when sailing and fishing. It is intended for general offshore and rough-weather use when a high standard of performance is required. It should turn an unconscious person onto his or her back and requires no subsequent action by the wearer to keep his or her face out of the water. Its performance may be affected if the user is wearing heavy and/or waterproof clothing.
The 275N lifejacket 
The 275N lifejacket is recommended for offshore cruising, fishing and commercial users. It is intended primarily for extreme conditions and for those wearing heavy protective clothing that may adversely affect the self-righting capacity of other lifejackets. It is designed to ensure that the wearer is floating in the correct position with his or her mouth and nose clear of the surface of the water.
Lifejacket types in the United States 
The United States Coast Guard gives the following information about Class I, II, III, and V lifejackets:
Type I PFDs / Off-Shore Life Jackets 
This type of life jacket is best for all waters, open ocean, rough seas, or remote water, where rescue may be slow coming. Appropriate for commercial abandon-ship situations for commercial vessels and all vessels carrying passengers for hire, as well as recreational boating.
- Inherently Buoyant Type I PFDs - SOLAS Service
- Inherently Buoyant Type I PFDs - U.S. Service
- Inflatable Type I PFDs - SOLAS and Domestic
- Hybrid Type I PFDs - US Services
Type II PFDs / Near-Shore Buoyant Jackets 
This type of life jacket is best for general recreational boating activities in calm, inland waters, or where there is a good chance for fast rescue:
- Inherently Buoyant Type II PFDs
- Inflatable Type II PFDs
- Hybrid Type II PFDs
Type III PFDs / Flotation Aids 
This type of life jacket is best for general recreational boating or specialized activity that is marked on the device such as water skiing, hunting, fishing, canoeing, kayaking and others. Good for calm, inland waters, or where there is a good chance for fast rescue. Designed so that wearing it will complement boating activities:
- Inherently Buoyant Type III PFDs
- Inflatable Type III PFDs
- Hybrid Type III PFDs
Type V PFDs / Special use devices 
This type of life jacket is used only for special uses or conditions. Instructions and limits should be followed according to the label on the life vest or device.
- Hybrid Inflatable PFDs
- Canoe/Kayak Vest
- Boardsailing Vests
- Deck Suits
- Work Vests for Commercial Vessels
- Commercial Whitewater Vests
- Man-Overboard Rescue Devices
- Law Enforcement Flotation Devices
- "NASBLA - The National Association of State Boating Law Administrators". Retrieved 2012-03-18.
- "Foundation Findings #50 - The Life Jacket Test". Retrieved 2012-03-18.
United States 
- ABCs of PFDs, basic info, US
- BoatsUS tips on selecting the right lifejacket
- "Life Jacket Wear / Wearing your Life Jacket / US Coast Guard Boating Safety". Retrieved 2012-03-18.
- United States Coast Guard: Personal Floatation Device Selection, Use, Wear and Care, more detailed information, including commercial requirements
- How to Choose the Right Lifejacket, video from West Marine, 11:29 min.