Penguins have two areas where their body is very poorly insulated and where they can lose a lot of heat, these are their flippers and their feet. These regions give penguins at the same time a problem and a solution. A problem because of the heat loss, and a solution because they can be used for cooling down. It's all well and good being brilliantly insulated, but when you use a lot of energy and so generate heat, or the temperature rises, not being able to lose that heat becomes a big disadvantage in itself.
The solution is really quite elegant. The muscles that operate feet and flippers are not located in the feet and flippers, but deeper in the warmer regions of the penguins body. The feet and flippers are moved by tendons that pass through them and attach to toes etc. like a sort of remote operation by wire or string. This means that it doesn't matter if the feet and flippers get really cold as they can still be operated normally by regions that are fully functional and at normal body temperature.
Penguins have a heat-exchange blood-flow to these regions. The warm blood entering the feet or flippers flows past cold blood leaving so warming it up in the process and cooling the blood entering at the same time. Blood in these parts is significantly colder than in the rest of the body. By the time the blood re-enters the rest of the body it has been warmed up and so doesn't have so great an effect on the core body temperature.
Penguins feet are never allowed to get below freezing point, blood flow is finely adjusted so that they are kept just above. When it gets very cold, the feet are covered by the feathers and fat layer of the body so they are not exposed to cooling winds. So while a man standing barefoot on ice would quickly get frostbitten, penguins can do so all their lives with no damage at all.
At low temperatures or when in the sea, the blood flow to feet and flippers is very low anyway so reducing heat loss further. When the penguin needs to lose heat quickly, the blood flow to these extremities is increased and so lots of warm blood enters them which cools quickly so dumping excess heat rapidly and efficiently.
From Cool Antarctica @
Photo from Flickr