UK professor says smearing yogurt on your windows can cool your home

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.

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?