Cold hole

In ad hoc outdoor shelters, a cold hole is the practice of deliberately creating a space for the cold air to gather, at a lower level than where people sleep.

Cold holes exploit the fact that cold air is denser, which makes hot air rise. A cold hole is generally used in improvised winter shelters, such as igloos. Cold holes can be just that – holes in an otherwise level floor. Alternatively, the cold hole can be the lower level in the igloo, typically where the entrance is; a higher level would be built at the back of the igloo, where people sleep.