> Researchers at the University of Sydney and commercial start-up Dewpoint Innovations have created a nano-engineered polymer coating that not only reflects up to 97% of the sun's rays, but also passively collects water. In tests, it was able to keep indoors up to 6 °C (~11 °F) cooler than the air outside.

So "blocks" is a poor word choice - tarpaper will block 97%+ of light.

I see nothing about the cost / durability / toxicity of the new paint-ish coating. Hopefully that's "low" / "very" / "non-".

As far as the "non-" you might look at

From https://en.wikipedia.org/wiki/Polyvinylidene_fluoride#Safety...

"PVDF is widely considered safe and ubiquitous used for water treatment,[24] the food industry, and biocompatible devices like hernia meshes or internal devices.">

They did say that the material didn't degrade over the course of their testing, but of course that's only a year or so.

> the coating withstood the challenging test of the harsh Australian sun, and showed no signs of degradation over the six months.

Real-world optimal would be 25+ years - in environments with acid rain, bat/bird droppings, hailstones, heavy smog, ice dams, 65° C summers, and several other sorts of hazards.

(Yes, that's a ridiculously big ask. OTOH, the planet we're stuck on is starting to char. And workable Planet B's are looking extremely scarce):

I do not have any polyvinylidene fluoride-co-hexafluoropropene (PVDF-HFP) but I wonder if there is a similar DIY option. It sounds like it uses little bubbles in the paint to reflect the sunlight. I would really like something like this here in Texas. It is getting dryer and I worry about our well.