system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I wanted to keep a kitty on my lap as warm as possible, would I want to be super muscular or really fat?
gpt
Fat itself is insulating. Since your internal temperature is the same regardless of muscle or fat (high internal temperature means you are having a fever, low means hypothermia), having extra fat keeps that temperature from escaping. This makes your skin temperature lower if you were fat versus if you were muscular. The kitten would feel colder due to the colder skin on a fat person.

There is an exception if the person was so fat that they could cover the kitty in their fat folds... then the fat insulates in the heat generated by the kitten (though this would be very uncomfortable for the kitten and may suffocate it).