I'm a vessel examiner with the US Coast Guard Auxiliary. An earlier responder correctly related that an inflatable pfd is valid only if it is being worn. There is a new type III inflatable that does not have to be worn to be legal, but most policing agencies aren't aware of it yet, so if you have one, I suggest you wear it regardless. The Coasties we work with on the Mississippi gulf coast all wear auto inflatables, and don't seem to have problems with improper inflating due to water exposure. I think the newer models handle water better than those from a few years back. Bottom line... wear a pfd, period.