Extreme cold weather clothing

Extreme cold weather clothing is clothing for arctic or mountainous areas. Its primary function is to trap air as an insulator to prevent heat loss from the wearer's body. Secondary and necessary is to conduct water vapor away from the body to keep the insulating layers dry. A shell keeps the wind from disturbing the still air in the insulating layers. In warmer conditions, the shell protects from water intrusion.

The U.S. National Weather Service defines extreme cold as −35 °F (−37 °C) with winds less than 5 miles per hour (2.2 m/s).^[1] In these conditions, the unprotected skin of a healthy adult will develop frostbite in ten to twenty minutes. The Canadian standard includes even lower temperatures.