Vincent Parasie, architect: “Covering windows with aluminum foil is an emergency solution against heat”

As an intense heat wave grips southern Europe, and across parts of the United States, demand for fans, air conditioners, awnings and other cooling devices has surged as people look for ways to make indoor temperatures more bearable.

What is the aluminum foil window trick?

But for homes where those options aren’t practical – whether because of cost or limited space – Paris is offering an unexpected alternative.

Across the French capital, many windows have been completely covered with aluminum foil to help block heat from entering buildings. From a technical standpoint, the idea has some scientific backing, as aluminum reflects between 95% and 98% of solar radiation, reducing the amount of heat that passes through the glass.

Speaking to La Vanguardia, architect Vincent Paraise described the technique as “an improvised, inexpensive and superficial emergency solution against the heat,” adding that its appeal lies in its low cost and the fact that it is quick and temporary to install. Even so, he recommends placing the foil on the outside of the window, “so it acts like a thermal mirror.”

Even then, this is not a solution that should remain in place for more than a few days. Although aluminum foil can provide short-term benefits – including helping repel birds, protecting furniture from direct sunlight and reducing energy use – it also comes with drawbacks.

If the foil is attached to the inside of a window, heat can become trapped between the foil and the glass, increasing the risk of the pane cracking or even shattering. It is also visually unappealing and completely blocks natural daylight, something that has been linked to mental health problems when homes remain without adequate sunlight for extended periods.

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