Type IV PFD refers to the 4th level of the United States Coast Guard's (USCG) classfication for personal flotation devices. Type IV PFDs are carried on boats as a device that can be thrown to a drowning person. These are either the circular rings found on commercial boats or around swimming pools. On recreational motor boats, these take the form of seat cushion style devices. They are not meant to be worn.
Read More about the USCG PFD Specifications