Fat test for keeping warm

Before the lesson make bags of fat:
Put half a block of lard in a medium ziplock baggie, and flatten it out.
Zip closed, then zip inside a second baggie.
Make a second control set with no fat: two baggies, one inside the other.

Hold the fat bag on your hand, then place a bottle of iced water on top of it.
Do you feel cold? (No)
Then do the same with the control bag. Do you feel cold? (Yes)
The fat is insulating and will stop you from feeling cold.

(Traditional 'blubber glove' has the same baggies of fat but you can put your hand inside: https://stevespangler.com/experiments/blubber-gloves/
I found that with young students, iced water often spilled into a blubber glove when they pushed it into the iced water.)

When bears hibernate, and the temperature outside is really cold (way colder than this water). They have a layer of fat under their skin which insulates them from the cold (it stops the cold from leaving their bodies).
Feel your fat under your skin by pinching your skin. Your fat is less than a cm thick. Hibernating black bears have a fat layer about 4cm thick. Polar bears have a fat layer up to 11 cm thick.

Background information: heat moves through fat half as fast as through muscle or other kinds of water-based body tissue. But for animals keeping warm, passive heat conduction rates is probably less important than controlling the paths of blood flow through the body e.g. using counter-current systems. Fat tissue near the skin can survive for hours without any blood going through it.