Air has a low thermal conductivity while being very mobile. There are two elements of cold air that are important to protect against:
1. Prevent the cold wind from penetrating and replacing the layer of warm air close to the body, especially the upper body.
2. Create a layer of still air which will serves as insulation, by putting dry leaves in the clothing. The body continually warms the layer of air close to the body.
You want to warm the center parts of the body first—chest, neck, head, and groin. Areas with large blood vessels, such as the head, neck, chest and groin, will usually loss more heat first because larger blood vessels do not constrict as effectively as the smaller ones near the skin.