Question

How do the hair of certain animals help
in keeping their bodies warm

Answer 1

as in the case of polar bears, heat from their body is trapped by their hair and outer cold wind is not allowed to enter by these hairs .So in this way heat is trapped in the body and cold wind doesn't touches the body making their bodies warm

Answer 2

they act as insulators.
they do not allow the body heat to escape the body and thus help in keeping their body warm.
Eg. polar bears have hair on their body that keep them warm and hence to survive in such low temp. condition.