Polar bears, whales, seals, and other arctic creatures have a layer of fat under their skin that helps keep their heat in when it's cold, and especially when they dive into water that's just above 0° C. This layer of fat is called blubber. Here's a simple experiment you can try, that will show you that blubber really can keep you warm.
You'll need a package of Crisco, lard, or other fat, two zippable sandwich bags, and a bowl of ice water with ice cubes.
Put your hand into the bowl of ice-cold water. How long can you keep it there? If you had to swim in this water, all the heat from your body would escape into the water and you would quickly freeze to death. So would a polar bear.
Let's see if blubber helps.
Spoon almost a full package of the lard into one of the sandwich bags.
This lard is very similar in composition to the fat under an arctic animal's skin. In fact, animal blubber can be eaten, cooked with, and even burned in oil lamps.
Inuit peoples in the north used it to help survive the cold weather.
Place your hand inside the second empty sandwich bag. This is just to keep your hand clean, and to keep the lard clean as well, so that it can be put back in the box and used again.
If you don't mind getting messy, and don't plan to reuse the lard, skip this step.
This is the fun part! Bury your hand inside the bag containing the lard. Wiggle your hand right down inside, until it is surrounded on all sides by lard. Use your other hand to mold the lard around your buried hand, making sure it is covered by a thick layer on all sides.
We couldn't find large sandwich bags, so it was a tight fit. Try to use bags that will fit your hand. Move the lard around so your hand is buried on all sides.
And now, the test! Immerse your lard-protected hand in the bowl of ice-water. Remember how cold it was?
Amazing, isn't it? Your hand stays warm. You can't feel the cold at all! You could leave your hand immersed in the water for a long time, and it would never get cold!
This is how seals, polar bears, and whales can swim in ice-cold water and not freeze to death. The layer of fat, called blubber, under their skin, keeps the heat in. They don't feel the cold at all!