Originally Posted by Wuwei
I have read that too, but I find it really hard to believe. It seems to defy common sense. You can feel the difference yourself when you touch something black and something white that have been sitting in the sun for awhile. When I lived in the south I couldn't touch my steering wheel (black) if the car had been sitting in the sun for awhile, but the body of the car (white) was comfortable to the touch. I read a study somewhere that said if everyone in the south just painted the roofs of their houses white there would be a huge energy savings.
There's a little more to consider. If the helmet was completely closed and had a greenhouse of windows installed all around it, with objects and materials inside that would absorb the heat, then it would get just as hot as the inside of your car.
Put a layer of foam over the interior surfaces of your car between the sun and the interior, vent it and fill the void with a liquid cooled object (like the rider's head in a helmet) and there will be less heat build up and better dissipation.
The riding suit I wear is black and it doesn't absorb heat at all. It's one of the properties of the material.
A dark painted helmet could become hot to the touch on the outside, but the inside remains essentially the temp of the rider's head.
It is easier and less expensive to paint a roof of a house with a IR reflective paint, or use a material that does not absorb and radiate heat, than it is to place an inch or two of foam between the roof surface and the attic space, the way a helmet is made.
Thermodynamics is an interesting thing to study and understand. There are a lot of aspects that can affect the transference and accumulation of heat.