It is worth mentioning that a wetsuit can be a critical item in surviving hypothermia. I am referring to a nice 1/4"thick custom tailored wetsuit with an integral hood, although anything neoprene helps. One guy floated around in our local water for more than 24 hours, before encountering an oil platform and hauling himself out. In another instance, an urchin boat sank - the divers aboard were wetsuited, others were not. A diver and his fiancee clung together for several hours. He was wetsuited;she was not. Eventually she expired and sank from sight. He was rescued.

If you are not a scuba diver, an immersion suit is probably the ticket....