France turns to white chalk window coating as heatwaves make shutters and fans ineffective

Record‑breaking temperatures across France have exposed the limits of traditional cooling methods such as shutters and ceiling fans. Homeowners are increasingly relying on air‑conditioning, innovative cooling technologies and greener building designs to stay comfortable.

At the same time, an old French trick has resurfaced: a paste made from white chalk (blanc de Meudon) is being applied to windows to reflect solar radiation. The inexpensive mixture of calcium carbonate powder and water creates a white film that cuts the heat entering rooms, with users reporting temperature drops of 1‑2 °C. The solution spread quickly during the heatwave, prompting shortages in stores and adoption in schools and private homes alike.

Experts note that while the chalk coating is not a complete fix, it offers a low‑cost, easy‑to‑apply way to reduce indoor heat while the country explores longer‑term architectural and environmental adaptations.