The French are painting their windows with chalk to beat the heat

3 hours ago

French residents are using crushed chalk (Blanc de Meudon) painted on windows to reflect heat and cool homes during heatwaves.
White surfaces, including chalk-based coatings, leverage radiative cooling by reflecting sunlight and emitting heat, with research showing ultra-white paint can reflect over 98% of sunlight.
Chalk's main component, calcium carbonate, is highly reflective and resistant to solar radiation, making it effective for cooling applications in paints and fabrics.
Demand for Blanc de Meudon has surged in France due to social media trends, leading to stock shortages as temperatures exceed 40°C (104°F).
White-painted cool roofs and windows offer a low-tech, sustainable alternative to air conditioning, reducing energy use and mitigating urban heat island effects.
Studies indicate cool roofs can lower temperatures significantly; for example, in London, they could prevent heat-related deaths by cooling areas during heatwaves.
Alternative DIY cooling methods include using yogurt on windows, which researchers found can reduce indoor temperatures by up to 3.5°C (6.3°F) in sunny conditions.

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