33 CFR §175.13

As used in this subpart: Personal flotation device or PFD means a device that is approved by the Commandant under 46 CFR part 160. Throwable PFD means a PFD that is intended to be thrown to a person in the water. A PFD marked as Type IV or Type V with Type IV performance is considered a throwable PFD. Unless specifically marked otherwise, a wearable PFD is not a throwable PFD. Wearable PFD means a PFD that is intended to be worn or otherwise attached to the body. A PFD marked as Type I, Type II, Type III, or Type V with Type (I, II or III) performance is considered a wearable PFD.