How do polar bears stay warm in Arctic winters?
user
Polar bears are incredibly well insulated with a layer of blubber that can be up to 10cm thick covered with another 15cm of fur.

Polar bears lose so little heat to their environment that they are almost invisible to thermal imaging cameras. But a University of Buffalo study found that polar bears have also evolved genes that produce more nitric oxide than other bear species. Nitric oxide is a signaling molecule and one of the mechanisms it controls is whether cells use their available nutrients to produce metabolic energy, or simply convert it into body heat. Polar bears seem to be able to divert more of their body’s resources into generating heat. This relies on them getting enough fuel for this process, and adult polar bears have a high calorie diet; they mostly eat seal blubber.
assistant
What the heck is a blubber?
user
Blubber is a thick layer of vascularized adipose tissue under the skin of all cetaceans, pinnipeds, penguins, and sirenians.
assistant