As air temperature falls below that
of the body, heat will be lost;
by radiation (more if sunburned),
by conduction (if lying in snow or ice or in water)
by convection (if air is able to blow heat away from the body)
Convection is usually the main cause of heat loss and this can be
minimalised by using clothing that traps the insulating air. The faster
the air moves the more heat it can drag away from any object - thus
windchill