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As it is getting warmer here by the minute I was asking myself:

Are there materials, that are black (in th visible range) but reflect (most) invisible light?

Furthermore, I asked myself what fraction of heat could be kept away using this material in daylight.

For bonus points, it would be great if it could be used as some kind of fabric. I am not looking for a specific material but am curious, as e.g. metals do reflect all light up to a certain frequency and thus would not suffy. Therefore it would be nice to understand the underlying mechanism.

In the winter of course it would be nice to reverse this, so to have white shirts, still getting hot in the sun.

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  • $\begingroup$ Not a proper answer, but when looking at an image of myself taken with an IR camera I was surprised to find that my black fleece top appeared white. So that kind of synthetic material might be an example, although I wouldn't want to wear it on a hot day! $\endgroup$
    – N. Virgo
    Jul 18, 2014 at 15:14

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As only about 50 % of the energy of the light is in the visible spectrum is in the visible area (Wikipedia) this should be at least theoretically possible.

So you would get with a close to perfect t-shirt only 50% of the energy. Whether such materials do exist, I don't know. I guess there are some materials fulfilling the condition, but I don't know whether they are cheap enough and flexible / light enough to be used as clothes.

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  • $\begingroup$ -1, the fact that was theoretically possible was clear, and the central part of the answer is basically "I don't know". $\endgroup$
    – DarioP
    Jul 20, 2014 at 13:23
  • $\begingroup$ Furthermore, I asked myself what fraction of heat could be kept away using this material in daylight. - I might could not answer every part of the question, but as there was no other answer, i decided to answer at least this part of the question that i could. So no, it was not clear. $\endgroup$
    – user3384414
    Jul 21, 2014 at 21:38
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There is apparently a whole industry dedicated to this (relevant google search near infrared reflective coating

For instance, see this paper in Thermal Performance: Special Infrared Reflective Pigments Make a Dark Roof Reflect Almost Like a White Roof by Bill Miller et al.

As user3384414 pointed out, nearly half of the solar radiance is outside the visible, e.g. (from wikimedia commons)

Solar radiation spectrum

We see that the near IR is much more important than trying to block the UV.

From the linked paper:

Solar reflectance with and without near IR coating

It seems that for black surfaces, these kinds of coatings can change the solar reflectance from around 4% to 40% or so, even higher than the untreated reflectance of the gray surface (20%).

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