French residents use chalk-coated windows to combat heat wave

During a prolonged heat wave in France, many residents have turned to a low‑cost method of cooling their homes by applying a layer of chalk powder, known as Blanc de Meudon, to interior windows. The calcium carbonate mixture, mixed with water, creates a white film that reflects a portion of ultraviolet and infrared radiation, helping to lower indoor temperatures.

The technique, popularised on social media, is being used in apartments, schools and other buildings as an inexpensive alternative to air‑conditioning, which consumes electricity and can increase urban heat. Experts note that while the method can reduce heat gain, proper insulation remains the most effective way to keep interiors comfortable during extreme temperatures.