Researchers at the Institute of Micro and Nanotechnology (IMN-CNM), part of Spain's CSIC, have developed a nanomaterial that can cool sun-exposed surfaces by up to 12.9°C without using any electricity. The innovation, published in the journal Nanophotonics, could offer a low-cost, passive alternative to air conditioning, which currently accounts for nearly 20% of global electricity consumption.
How passive radiative cooling works
The technique, known as daytime passive radiative cooling, exploits a unique property of Earth's atmosphere: a specific infrared window between 8 and 13 micrometres allows heat to escape directly into space. A material that strongly emits radiation in that band while reflecting solar radiation can become cooler than the surrounding air, with no energy input.
The team, led by the Functional Nanoscale Devices for Energy (FINDER) group, chose polyvinylidene fluoride (PVDF), a polymer already recognized for its heat-emitting capabilities. Cristina Vicente, a researcher at IMN-CNM and head of the COOLed project, explains that PVDF "brings together a combination of properties" that make it ideal: it emits heat efficiently, withstands ultraviolet radiation, repels water (giving it a self-cleaning effect), and is durable outdoors.
The key breakthrough lies in the material's nanostructure. The researchers infiltrated PVDF into nanoporous templates of anodised aluminium oxide, creating three-dimensional structures with precisely controlled internal geometry. This nanoscale design is crucial because the optical performance of such coolers depends on their architecture.
Impressive performance in real-world tests
The optimized version of the material, treated with ultrafast cooling after infiltration, reflects on average 82.4% of incoming solar radiation and emits 96.7% of heat in the 8–13 micrometre infrared window. On paper, this translates to a cooling capacity of 182.3 watts per square metre under solar irradiance of 1,000 W/m².
Field tests on the rooftop of the research centre in Tres Cantos, Madrid, confirmed these figures. During the hottest, driest days last summer, the treated surface stayed up to 12.9°C cooler than an uncoated sample. The material was first exposed to ultraviolet light, which whitens it and enhances its solar reflectance.
The researchers stress that the technology is still under development, but they point out that the manufacturing process is relatively inexpensive and compatible with existing industrial methods. This opens the door to applications ranging from building façades and roofs to electronic devices, vehicles, and even personal cooling systems.
As Europe grapples with rising energy costs and climate targets, passive cooling solutions like this could play a role in reducing dependence on air conditioning and the associated emissions. The development also highlights Spain's growing contribution to clean technology research, a sector that has seen increased investment in recent years.
While the material is not yet ready for commercial deployment, the team's results are a promising step toward a more sustainable approach to keeping cool in a warming world.
