Snake´s Super Shelter - one minute survival tip
Channel: SurviveSmart
Date: 2016-01-10

Double-covered shelters consist of two plastic sheets separated by a layer of air. Double covering has a major benefit over single covering (where there's just one cover of plastic sheet and no air layer): Keeps warm air in, meaning your emergency shelter is better insulated.
Double covering prevents heat transfer by convection. The trapped air is a very poor conductor which reduces the rate of heat loss through the cover. Therefore, the space in the shelter stays warmer for longer.