Personal flotation devices (PFDs) are like seat belts: they save lives. If you don't wear one, you’re an idiot — and risking your life unnecessarily. Everybody who gets in a boat, regardless of conditions or experience, should wear one. This is especially true for adventures where the water is cold, boaters are young, or some other element may rapidly accelerate a mishap into a life-threatening emergency. A good PFD (also called a life jacket or life vest) is arguably the single most important piece of boating equipment you can buy. So what should you be looking for?

Typecast
PFDs must meet certain requirements as established by the Coast Guard, which categorizes PFDs as Type I, II, III, IV, or V. (This designation should be clearly listed on the PFD.) Each type is designed for a different use, from commercial applications in rough seas (Type I) to life rings and other buoyant throws for larger vessels (Type IV). The vast majority of recreational PFDs are Type III, which hug the torso and provide excellent range of motion. They're good for most boating adventures, where rescue or help is likely in a short period of time. But be aware of their limitations: Unlike Types I and II, Type IIIs are not designed to keep an unconscious person's head above water.

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According to the Coast Guard, 505 people drowned in the U.S. in boating accidents in 2008; more than 90 percent (459) did not wear a PFD.

Thicker than Water?
If your lungs are full of air (adult lungs hold roughly 5 liters), you will float in the water, regardless of your body type and whether the water is salty or fresh. If your lungs were to completely deflate, however, you might sink. Roughly two-thirds of the population sinks in fresh water with lungs emptied; less than 5 percent sink in more buoyant salt water. (If you have low body fat, you’re more likely to go under.) The upshot of all this? PFDs need to supply only a small amount of extra buoyancy to keep you afloat, no matter what your bodytype. This number, measured in pounds, is usually listed with product specs. A Type III must provide a minimum of 15.5 pounds extra buoyancy; most hover in a narrow range between 16 to 18 pounds. Type I is the most buoyant (minimum 22 pounds).

Snug up
The best PFD is the one you wear. But for it to work, it's critical that it fits correctly. A properly fitting PFD wraps snugly around your torso and does not move in any direction. In particular, it will not slide upward toward your chin, especially when you're in the water. Shoulder and neck openings should provide an appropriate range of motion for your intended activity, especially if you'll be paddling. When trying one on, loosen all the straps. Begin tightening at the waist and work your way upward. Adjust shoulder straps last. Once properly adjusted, a PFD should feel snug but not restrictive. Have a friend lift up on the shoulders or grab from behind and shake you — the PFD should not move. If it does, tighten the straps or move on to another size or style.

Get Fit
PFDs range significantly in price, from less than $20 to $150 or more. And you get what you pay for, especially when it comes to fit. More expensive models feature multiple chest straps and adjustment points; a waist cinch cord; additional seams along the torso for a closer, more contoured fit; and ergonomically cut shoulder openings for a fuller range of motion. Women's models are available, and recommended, for those who need a contoured, non-flattening fit across the chest. Any inexpensive, properly fitting Type III will keep you safely afloat, but expect to pay $80-$120 for a quality PFD with good fit and features.