Yes, aluminum foil can be used over windows to help keep homes cool

https://www.localmemphis.com/article/news/verify/weather-verify/aluminum-foil-windows-cool-heat-wave/536-69a28e6f-0cef-4ae4-a730-fb29e42733a6

Emergency management agencies specifically recommend using aluminum foil-covered cardboard that goes between windows and drapes.

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People took to social media to share ways people in homes with no air conditioning or poor air conditioning could fight the heat and stay cool. One method in particular stood out because users claimed it was both cheap and effective: covering windows with aluminum foil to reflect sunlight and the heat back outside.

A TikTok video sharing the method got more than 100,000 likes and several tweets sharing the tactic received thousands of likes and retweets. All of the posts tell people to black out windows with aluminum foil.

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The Federal Emergency Management Agency (FEMA) published a June 29 blog post that included the aluminum foil tactic among six ways to combat extreme heat.

More at link.

Heat wave here in TN is brutal. 98-100F forecast for another 10 days, as far as my app projects. With near 100% humidity & a very high dew point every day, it is miserable outdoors.

For anyone interested, there is also attic foil. Various brands available. One friend paid ~$200 for a 1K sq ft. Roll (this friend is not a frugal shopper. I found a 1K sq ft roll for $93.) You staple the foil to roof rafters to reflect heat from roof away from house. The products I looked at have very good reviews & friend who installed it said it kept his upstairs a few degrees cooler.

Stay cool!