I used khakis. Jeans would work, just need a weave/material that's tight enough to hold air when wet.

These military trainees tied the pants legs together and splashed water to generate an air pocket.

http://youtu.be/E3VgMR5NWdU

Dad was a sailor, did two tours on an aircraft carrier. He taught me the pants trick back in the 70's. It works!

Or just wear your PFD.

Bingo!

The inflated jeans trick makes a nice YouTube stunt in a warm, calm pool, but I question how practical it would be in a real deal emergency? Consider that in most cases one would be wearing shoes or boots, which you would need to take off before you could start to take the pants off. Then you need to get the pants off. Then you need to knot both legs. Only then can you get some floatation.

Even slightly cold water will rapidly sap your strength and dexterity. Even moderate wave action will also make this harder. I would like to see a video of someone jumping fully clothed (including shoes) into 60 F water with a stiff wind kicking up a 2ft chop, and making this work. Until then I'm skeptical.

The best advice is still to wear your F-ing PFD!

Actually there was a Marine who went overboard in the Indian Ocean and he used this trick to stay afloat until he was rescued by a Pakistani fishing boat. As I recall he had been presumed dead until he phoned home.

Marine Survives 36 Hours At Sea Inflates Uniform Into Life Preserver After Falling Overboard

81 degrees is still 15 or so degrees cooler than humans, so eventually we'll get hypothermic. Just takes longer. Obviously worse the colder the water.

Re: drown proofing, you can also do the same thing with a long-sleeve shirt. The Navy made us do this in basic; I assume the USMC and USCG teach it as well.

Finally, it's a wonder these articles never mention people being laid up in the hospital with rhabdomylsis after such extended periods of activity. I'm curious how often this is really an issue.

Here's a chart the shows the expected time period of survival for a given temperature:

http://www.pfdma.org/choosing/hypothermia.aspx

Ireckon

Very informative. Thanks for the link.

These estimates are always highly approximate. As an alternative, perhaps slightly more optimistic, see Prof. Popsicle's (Gordon Geisbrecht) chart at
http://www.coldwaterbootcamp.com/pages/1_10_60v2.html. Note that this chart is in degrees C so you will need to convert to F. Also note that immersion hypothermia is one of the few areas where it is advantageous to be a bit overweight!

Note that these survival times assume you have floatation. Without a PFD, you rapidly loose strength and coordination, and it becomes inceasingly difficult to stay afloat. In most cases without a PFD or other floatation you will drown before dying from hypothermia.

A few years ago we had a remarkable case here in Alaska showing just how valuable a PFD can be even in very cold water:
Kenai girl credited with saving friends in Tustumena Lake accident. The girls were in the water for about 2 hours, and remained conscious and able to move towards shore, with water temperature of about 40-45 F (4-7 C).