PFD stands for personal flotation device and includes life jackets and throwable flotation devices.
In the United States, all recreational boats must carry one wearable life jacket for each person on board. While all life jackets must be U.S. Coast Guard approved, in good serviceable condition and be the appropriate size, the best life jackets are the ones the user will wear. The USCG uses a performance type classification system;
Type I offers the most buoyancy, is intended for rough water, and is designed to flip an unconscious person face-up;
Type II is most common for general boating activities in calmer water;
Type III are considered flotation aids;
Type IV includes throwable flotation aids;
Type V are special use PFDs, including inflatable life jackets, that can offer similar capabilities as a Type I, II or III.
The United States Coast Guard embarked on an effort to harmonize safety standards with Transport Canada in 2014. The goal was to change the terminology, labeling and testing procedures to match that of the rest of the world, with a goal to one day harmonize the US/Canadian markets with the European market.
While the previously approved PFDs under the Type classification system may remain in service, newer products are being tested to meet a performance level indicating the level of buoyancy;
Level 50 (11lbs) intended for near-shore use and offers the most mobility and comfort with good flotation for most people;
Level 70 (16lbs) has comparable buoyancy and application to a Type III PFD
Level 100 (22lbs) is comparable in buoyancy and application as a Type I PFD
How much buoyancy do you need?
Most adults only need 7 to 12 pounds of buoyancy to keep their heads above water.
The reason is that ~95% of the human body consists of water or fat, both of which are equal to or lighter than water. This means, most people only need enough buoyancy to support the remaining ~5% of their body weight.
Hence, a 200lb person only needs about 10lbs or 45 newtons of buoyancy.