Hypothermia is the lowering of the body's core temperature. Heat Loss is caused by conduction, convection, evaporation, and radiation. Water, snow, and the cold ground conduct heat from the body. Wind and rain convect heat. Evaporation dries sweat and wet clothes robbing the body of heat.
Radiation is for all practical purposes unstoppable.
To prevent hypothermia stay warm and dry. Carry extra clothes, wind and rain gear. Water draws heat 540 times faster than air, and even light winds have a serious cooling effect. Handle the patient as gently as possible, rough handling can cause death. Stabilize, and prevent any further injury to the patient.