My husband was a lifeguard when he was younger and one of the things they had to do was take off their pants, tie knots in the legs, zip, button and try to throw it over their heads to trap air in them. Then they used it as a floatation device. They just did this over and over again, in the middle of the lake for a long time.
It's hard to believe stuff like this works, but apparently it does. I'm so glad that I've never had to put it to the test!
Jeanne