T-COMF: The green zone is called the comfort zone and within this temperature range most people can sleep comfortably in their sleeping bag. T-LIM: The yellow zone is called the transition zone from comfort to risk. In this zone, a lot of people can sleep comfortably, but some will start to freeze. T-EXT: The red zone is the risk zone and is defined as a zone in which a person can experience severe cold and be at risk of hypothermia (dangerously low body temperature). For example, an average woman can withstand a maximum of six hours in this zone. Read more here!