The Bedouins, Arabs who inhabit the Sinai Desert, wear black robes -- a color choice that, according to modern physics, doesn't seem to make much sense. White robes would reflect away much more of the sun's radiation.
Research by three Harvard scientists has revealed that the Bedouins are neither crazy nor studid: The black robes turn out to be no warmer than white ones.
The scientific team measured heat gain by radiation, heat loss by convection, heat loss by evaporation, heat storage and metabolic heat production for a man wearing a white robe, a black Bedouin robe and a tan army uniform with shorts.
As expected, the black robe absorbed 2 1/2 times as much radiation as the white and 1 1/2 times as much as the tan uniform. But, surprisingly, there was essentially no differences in rates of net heat gain. The temperature at the surface of the black robe was five degrees hotter than the white, but all the extra heat was lost before it reached the skin.
The scientists, reporting in the British magazine Nature, concluded greater convective transfer of heat occurs through air spaces beneath the black robe. This is generated by a "bellows" movement of the robes as they flow in the wind, or from a "chimney" effect whereby cool air from below is pulled upward by the movement of the warmer air as it rises through the loosely woven fabric.