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There's an interesting guide on how to make radiative cooling paint from common ingredients complete with an explanation why it works:

https://www.youtube.com/watch?v=KDRnEm-B3AI

The catch is that such paint is not particularly robust, much less weatherproof.

Beats yogurt I guess, which tends to smell as it turns in sunlight.

I have roof windows and was wondering how much I could gain from panels painted like that, but most likely as much as I would using the next best thing - a window sunshade, which I'm using already.

I applied some reflective film to the inside of some of my windows today and it seems to have had some effect, though the window is pretty hot to the touch now and apparently this kind of film can cause windows to crack through thermal stress.

It makes sense for any coating to be on the outside of your window but I wonder how much better hanging a reflective space blanket outside would be than this yoghurt layer or similar.

This is old (2025).

Fortune links to a BBC article, which doesn't really provide any more detail about the testing conditions. I wonder if rubbing a bar of soap on your windows would reflect light and be easier to wash off. Also, were the windows tested low-E or not?