[poulpy123]

I would put mylar sheets on my windows instead, although the best is of course to have shutters The traditional shutters from south east France are great to block the sun but still allow light https://volets-thiebaut.com/modules/boixmultiblocs/images/7a...

[pseudohadamard]

You can also get UV/IR-reflective coatings on your windows, either in the glass when they're installed or as aftermarket foils on existing ones. We have them on all of our sun-side-facing windows and they do a great job. They also provide privacy if you use the heavier-duty commercial-grade ones, which look like a mirror from the outside.

[nom]

emergency blankets works great and are cheap too

however, you get even better cooling with a coating that radiates the heat, it cools below the air temperature which feels so wrong

NighthawkInLight on YouTube has explored this and created recipes, the results still feel impossible to my intuition