system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we sleep better in a cold room but still under warm covers?

Why both warm *and* cold?
gpt
Your metabolism slows down during the night, your body naturally cools down a bit. A cooler room will enable you to sleep better as your body is closer to the temperature of the room, thus you're more comfortable. 

Under the sheets you get an insulating air pocket that's very close to your current body temperature which helps you not lose any more heat than your body wants. 

I think you're mistaking how the body determines temperature which is why this seems confusing. 

You tell the temperature based on the rate of heat loss or gain from the surroundings. The larger the difference, the faster the rate so the "hotter" or "colder" it feels. 

The sheets help lower this rate so you reach homeostasis with the surroundings, and you want a cool room so that you can reach homeostasis with what your body "wants" during the night.