This guide has been brought to you by Overton's.

Type I (Offshore Life Jacket) 22 lbs. bouyancy
Where: Best for open, rough or remote water, where rescue may be slow coming.
Advantages: Floats you the best.  Turns most unconscious wearers face up in the water.  Highly visible color.
Disadvantages: Bulky.
Sizes: Two sizes to fit most children and adults.

Type II (Near Shore Bouyant Vest) 15.5 lbs. bouyancy
Where: Good for calm inland water or where there is a good chance of a fast rescue.
Advantages: Will turn many unconscious wearers face up in the water.  Less bulky, more comfortable than Type I.
Disadvantages: Not for long hours in rough water.  Will not turn some unconscious wearers face up in water.
Sizes: Infant, Child-small, Child-medium, Adult

Type III (Flotation Aid) 15.5 lbs. buoyancy
Where: Good for calm, inland water or where there is a good chance of fast rescue.
Advantages: Generally the most comfortable.  Freedom of movement for water skiing, small boat sailing, fishing, etc.  Available in many styles, including vests and flotation coats.
Disadvantages: Not for rough water.  Wearer may have to tilt head back to avoid face down position in water.
Sizes: Many individual sizes from child small to adult.

Type IV (Throwable Device)
Where: For calm, inland water with heavy boat traffic, where help is always nearby.
Advantages: Can be thrown to someone.  Good back up to wearable PFD.  Some can be used as seat cushions.
Disadvantages: Not for unconscious persons.  Not for nonswimmers or children.  Not for many hours in rough water.
Kinds: Cushions, rings, and horseshoe buoys.

Type V (Special Use Device)
Where: Only for special uses or conditions.
Advantages: Made for specific activities.  Varieties include boardsailing, vests, deck suits, work vests and others.
Disadvantages: See label for limited use.

Type V (Hybrid Device)
Required to be worn to be counted as a regulation PFD.
Advantages: Least bulky of all types.  High flotation when inflated.  Good for continuous wear.
Disadvantages: May not adequately float some wearers unless partially inflated.
Performance level: Equal to Type I, II or III performance as noted on label.