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The Straight Dope ran an explanation of why nomads often wear black clothing - it absorbs heat better from the body. On the other hand, white clothing reflects sunlight better. Is it possible to get the best of both worlds and wear clothing that is black on the inside and white on the outside?

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Something to clarify: Cooler than what? Is white and black cooler than just black? Cooler than naked? –  endolith Nov 26 '10 at 18:41
@Endolith: Cooler than wearing either pure black or pure white –  Casebash Nov 26 '10 at 21:57
It all depends on whether you mean "cooler" or "kewler". –  Gordon Feb 3 '11 at 5:13
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3 Answers

The color of a surface doesn't reliably indicate the emissivity at non-visible wavelengths. The color in the visible spectrum is more of a side effect than anything. Most thermal radiation around body temperature or room temperature happens in the infrared region, not the visible, and that's not reliably indicated by visible color:

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The transparent glasses are opaque to the body's infrared emissions, while the opaque trashbag is transparent to infrared.

The emissions of the sun, on the other hand, occur mostly in the visible region, which could explain the common perception that white reflects and black absorbs. In the case of sunlight, this is probably the dominant effect.

But humans are too cold to radiate visible light.

For example, white paint is quoted as having an absorptivity of 0.16, while having an emissivity of 0.93. This is because the absorptivity is averaged with weighting for the solar spectrum, while the emissivity is weighted for the emission of the paint itself at normal ambient temperatures. ... The white paint will serve as a very good insulator against solar radiation, because it is very reflective of the solar radiation, and although it therefore emits poorly in the solar band, its temperature will be around room temperature, and it will emit whatever radiation it has absorbed in the infrared, where its emission coefficient is high. http://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation

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Since outside interacts with the radiation both ways, it would not help. But, there's something that would:

You need to have clothes which are Black (totally absorbing) in visible light and White in Thermal-infrared wavelengths (totally reflecting). This color is called Red (well, to some extent: if you shift the spectrum into visible terms).

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Could you provide a source to this? –  aitchnyu Sep 26 '13 at 9:52
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Since both absorption and radiation depend on color in the same way, this would decrease the energy that is radiated off into the surroundings. So if radiation were the only way to lose heat color wouldn't matter, and in the long term you'd have the same temperature as the incoming light.

But since nomad's don't live in vacuum there are other ways of heat transportation. What color is best depends on which forms of energy transportation dominate.

Since I guess that you lose more heat to other sources than radiation, while a large part of the incoming heat comes from light, making them white on the outside and black on the inside could make sense. But there are complicating factors such as wind, vaporization of sweat,...

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