As Cody Emphasizes in his book, we are ideally maintaining a temperature of 98.6 in that thin microclimate on the skin's surface. The failure is when to much sweat remains without transpiring off. Remember that water has zero insulating value and will rapidly fall to the surrounding temperatures. This is when hypothermia is accelerated by our own system. A glaring example is the strategy of Vapor Barrior Clothing. The theory here is warm sweat is trapped by non permeable materials and makes for a warm, if wet and smelly cocoon. The failure is when the clothing is eventually removed or vented. Then all that warm sweat rapidly becomes very cold and the body actually loses a greater reserve of internal heat very quickly.