Still air is an excellent insulator, while water is an excellent conductor. Heat conduction in water is about 25 times greater than in air. For example, heat transfer from skin to moving air or water. Wind chill index - gives the equivalent still air temperature for a particular ambient temperature at different wind velocities. The temperature gradient between the skin and air and the air velocity are important factors in determining convective heat loss. Because the superficial blood vessels in the head do not constrict in the cold, the head is an important source of heat loss - accounts for 30 - 35% of total heat loss at rest. Behavioural responses to the cold are important - clothing, seeking shelter, starting a fire, etc. Factors affecting responses to cold: skinfold thickness. The thicker the fat layer, the greater the insulation: gender. The average female has more subcutaneous fat than the average male (cid:198) more insulation.