As extreme heatwaves and rising temperatures become increasingly common, keeping buildings cool during the summer months has become both a public health priority and an environmental challenge. Traditional air conditioning systems, while effective, contribute significantly to energy consumption and carbon emissions. In response, scientists are exploring passive cooling alternatives that work without electricity.

One promising solution comes in the form of a bioplastic film that can dramatically reduce building temperatures by reflecting nearly all incoming sunlight. Developed by researchers at Zhengzhou University in China and the University of South Australia, the material reflects 98.7 percent of sunlight and passively cools surfaces by up to 9.2°C (16.56°F) in laboratory conditions.

The cooling film is made from polylactic acid (PLA), a biodegradable plastic derived from plants. It is produced using a low-temperature phase separation technique that gives it a highly reflective structure. Unlike many existing passive cooling materials that rely on petrochemical-based polymers or ceramics, this bioplastic provides an environmentally friendly alternative.

Field tests of the material have shown strong performance in real-world conditions. During daytime hours, the film achieved an average temperature drop of 4.9°C (8.82°F), with 5.1°C (9.18°F) observed at night. Additionally, it proved stable under harsh conditions. In a 120-hour endurance test simulating high UV exposure and acidic environments—equivalent to approximately eight months outdoors—the film retained its cooling effectiveness with temperature reductions up to 6.5°C (11.7°F).

Simulation models suggest that widespread use of this technology in urban areas could significantly reduce energy demand. For example, applying the film across buildings in Lhasa, the capital of China’s Tibet Autonomous Region, could cut air conditioning use by more than 20 percent.

This bioplastic innovation joins a growing field of passive cooling technologies, including the recently developed “world’s whitest paint,” which reflects 98.1 percent of sunlight and cools surfaces by 4.4°C (7.92°F) during the day and 10.5°C (18.9°F) at night.

As researchers continue to refine these materials and explore scalable applications, passive radiative cooling technologies could play a critical role in reducing energy use and helping cities adapt to a hotter future—without relying on electricity.