Cool roofs can reduce building cooling demand by reflecting sunlight and releasing heat, but their performance often declines as roofing materials age and accumulate dust. A research team has now developed a scalable bilayer roofing membrane designed not only to provide strong initial cooling performance, but also to maintain its optical properties during long-term use.
The study, accepted for publication in Science Bulletin, reports a multiscale-engineered polyolefin composite consisting of a titanium dioxide-loaded thermoplastic polyolefin, or TPO/TiO 2 , substrate and a thin propylene-based elastomer/boron nitride, or PBE/BN, surface layer. Unlike many radiative-cooling materials that rely on complex fabrication methods, the new membrane can be manufactured by an industrially compatible co-extrusion process. This approach enables continuous and large-area production, providing a potential pathway from laboratory-scale materials to practical roofing membranes. The TPO/TiO2 substrate strongly reflects visible and near-infrared sunlight, while the PBE/BN surface layer improves ultraviolet reflection and mid-infrared thermal emission. Together, the optimized membrane achieved a solar reflectance of 94.1% and a mid-infrared emissivity of 90.7%. The researchers also focused on a major challenge facing cool roofs: surface contamination. Dust that adheres to a roof can increase solar absorption and gradually weaken its cooling effect. Microscopic measurements showed that the PBE-based surface had much lower adhesion than the conventional TPO surface. By reducing high-adhesion regions where particles can become trapped, the surface layer limited dust retention and allowed the membrane to preserve more of its solar reflectance after contamination and rinsing. This microscopic control of surface adhesion translated into improved long-term optical performance. After 2,800 hours of xenon-arc accelerated aging followed by contamination, the bilayer membrane retained a solar reflectance of about 86%. After 5,600 hours of accelerated aging and subsequent contamination, it still retained about 83%, or approximately 88% of its initial value. Under the GB/T 18244-based protocol adopted in the study, 5,600 hours of xenon-arc aging corresponds to a ten-year-equivalent exposure. The researchers emphasize that this is a protocol-based accelerated-aging equivalent rather than ten years of direct natural outdoor exposure. Even so, the retained reflectance exceeded representative aged commercial cool-roof benchmarks used for comparison in the study. The membrane also remained stable after exposure to acidic, alkaline and saline environments, supporting its potential for use under different outdoor conditions.
To test whether the material's optical performance translated into real-world cooling, the researchers conducted an 84-hour rooftop experiment in Beijing. Compared with an uncovered asphalt roof, the membrane reduced roof surface temperature by an average of 9.4 degrees Celsius between 11 a.m. and 3 p.m. The maximum temperature reduction reached 18.1 degrees Celsius. The researchers further evaluated long-term energy-saving potential using building-energy simulations in eight cities representing different climates, including Beijing, Guangzhou, Sanya, Hong Kong, Miami, Dubai, Bangkok and New Delhi. In the tenth year of simulated service, buildings using the bilayer membrane required less cooling energy than those using the commercial cool-roof reference in all eight cities. The simulations indicated an average annual cooling-energy saving of about 10%, equivalent to approximately 71.5 megajoules per square meter, compared with the commercial membrane.
The findings suggest that long-term cool-roof performance depends not only on achieving high initial solar reflectance, but also on preventing reflectance losses caused by aging and contamination. By combining optical design, surface adhesion control and scalable manufacturing in a single membrane, the study offers a practical strategy for developing more durable, energy-saving roofing materials.
The research was conducted by researchers from Beijing University of Chemical Technology, Beijing Forestry University and Beijing Oriental Yuhong Waterproof Technology Co., Ltd.
Science Bulletin
Experimental study