In the sweltering, permanently air-conditioned city-state of Singapore, scientists have completed one of the most ambitious real-world tests yet of a deceptively simple climate technology: paint. A team at the National University of Singapore applied solar-reflective “cool paint” to the façades of seven operational campus buildings, covering nearly 50,000 square meters of wall surface, and then measured — at the scale of the wall, the building, and the entire neighborhood — exactly how much cooler and more energy-efficient the painted environment became. The results, published in the journal Results in Engineering, offer the strongest field evidence to date that reflective façade coatings can cut building cooling demand while modestly lowering ambient air temperatures in dense tropical cities.

The urgency behind the experiment is hard to overstate. More than half of humanity now lives in cities, a share projected to reach 68 percent by 2050, and urban areas consume over two-thirds of global energy while producing more than 70 percent of carbon dioxide emissions. The replacement of vegetation with concrete and asphalt has given rise to the urban heat island effect, in which cities become localized heat traps, driving up demand for energy-hungry air-conditioning and feeding a vicious cycle of warming and emissions. In Singapore, where daily temperatures hover between 23 and 33 degrees Celsius year-round, buildings account for more than a third of national electricity consumption, and air-conditioning alone consumes 60 percent of the electricity used in office buildings.

Cool paints, also known as solar-reflective or radiative cooling coatings, attack this problem at its source. These specialized materials combine high solar reflectance — bouncing incoming shortwave radiation back toward the sky — with high thermal emissivity, allowing surfaces to shed accumulated heat efficiently. While the technology has been studied extensively on roofs, where solar exposure is greatest, rooftop space in modern cities is increasingly monopolized by photovoltaic panels and mechanical equipment. Façades, with their vast combined surface area, have emerged as the next frontier. Yet until now, most evidence for cool façades came from laboratory mock-ups, scaled-down street canyon models, or computer simulations — not from real, functioning buildings occupied by real people.

That is the gap the Singapore team set out to close. Between July and October 2024, researchers coated the façades of seven buildings at the university’s College of Design and Engineering with a commercially available water-based acrylic solar-reflective paint, applied as one sealer coat and two topcoats roughly 40 micrometers thick. Crucially, the paint was not the blinding white typically associated with cool coatings. Each building received a palette of two to three muted colors, a pragmatic choice that preserved campus aesthetics and reduced glare risk while still raising the solar reflectance of the walls well above the baseline of 0.31 recorded before the intervention. Measurements with solar reflectometers showed the new finishes achieved reflectance values between 0.45 and 0.73, depending on location and color.

Building E1A, a seven-story institutional structure with an unshaded southwest-facing façade, became the centerpiece of the study. Calibrated thermocouples attached to the walls of E1A and a nearby unpainted control building revealed dramatic thermal changes. The painted façade ran up to 7.1 degrees Celsius cooler on its exterior surface, with a weekly average difference of 1.7 degrees, while interior wall surfaces were up to 3.3 degrees cooler. Heat flux calculations showed that total conductive heat gain through the painted wall fell by 33 percent over a week of measurements — and by 44 to 48 percent on sunny days. In essence, the paint transformed a wall that had been quietly baking the building’s interior into a far less enthusiastic conduit for tropical heat.

The energy consequences were measurable where it matters most: at the air-handling unit. Researchers instrumented Level 3 of E1A, a fully air-conditioned floor operating on a fixed 25-degree setpoint, and compared three weeks of cooling-load data before the intervention with three weeks after, carefully excluding the university’s summer vacation period and matching periods of near-identical weather. Average daily cooling load dropped 7.4 percent, from 250.3 to 231.7 refrigeration ton-hours. On sunny weekdays — excluding Mondays, when loads peak for operational reasons — the reduction reached 12.4 percent, and during the hottest hours between 9 a.m. and 3 p.m., hourly cooling demand fell by as much as 26 percent. Because Singapore’s grid remains fossil-fuel dominated, every kilowatt-hour of avoided cooling translates directly into avoided carbon emissions.

But reflective coatings carry a well-known scientific controversy: by bouncing sunlight off walls, do they simply blast pedestrians with reflected heat? To find out, the team installed thermal comfort stations 40 centimeters from both a freshly painted wall and an unpainted one, measuring air temperature, globe temperature, wind speed, and both incoming and reflected shortwave and longwave radiation. The painted wall indeed reflected 62 percent of incident shortwave radiation in the late afternoon, compared with 32 percent for the unpainted wall, and its surface ran up to 6 degrees cooler at midday. Yet the feared penalty proved modest: daily average air temperatures near both walls were identical at 30.2 degrees Celsius, and only brief afternoon peaks in globe temperature and mean radiant temperature showed slight increases. The cooler wall emitted less longwave radiation, partially offsetting the extra shortwave reflection.

To capture the paint’s effect on the wider neighborhood, the researchers borrowed a tool from economics: the difference-in-differences method, a quasi-experimental regression technique best known for evaluating minimum-wage policies. Five weather stations were deployed across the campus, two within the cool-painted precinct and three outside it, logging air temperature, solar irradiance, wind speed, and humidity at one-minute intervals from January 2024 to June 2025. By comparing how temperatures changed at treated versus control stations before and after the painting — while statistically controlling for solar radiation, wind, and rainfall — the team isolated the causal effect of the paint from the noise of Singapore’s variable weather.

The verdict: cool paint lowered average ambient air temperature by approximately 0.27 degrees Celsius across the full 24-hour cycle, with statistically significant cooling of 0.4 to 1.0 degrees Celsius during the peak solar hours between 10 a.m. and 5 p.m. The extended regression model, which achieved an adjusted R-squared of 0.535, showed coefficients behaving exactly as physics demands — every 100 watts per square meter of additional solar irradiance raised air temperature by about 1 degree, while wind and rainfall lowered it. The hour-by-hour analysis confirmed that the cooling effect was strongest precisely when the sun was strongest, a pattern consistent with the paint’s radiative mechanism rather than any spurious weather trend.

The findings arrive with important caveats. Energy savings were measured on a single air-conditioned floor with fixed schedules; comfort measurements were taken on roof podiums rather than pedestrian streets; and the coatings were newly applied, leaving the question of long-term reflectance degradation — a known issue for all cool surfaces — open for future study. Nevertheless, the researchers argue the practical implications are immediate. Because façade repainting already happens on roughly seven-year maintenance cycles, embedding solar-reflective coatings into routine repainting offers a nearly cost-free decarbonization lever, especially for buildings with west-facing walls, dark paint, and minimal shading. Pairing cool façades with louvers, greenery, and arcades can manage the modest radiant penalty near walls. And in a warming century where two-thirds of humanity will live in cities by 2050, the idea that a coat of paint — applied by ordinary contractors, on ordinary buildings, on an ordinary maintenance schedule — can measurably cool both the grid and the street may prove one of the most quietly scalable climate interventions yet tested.

Subject of Research: Field-scale evaluation of solar-reflective cool façade paints on operational buildings and urban microclimate in tropical Singapore

Subject of Research: Technology and Engineering

Article Title: Multi-scale evaluation of cool façade paints for tropical built environments: real-world impacts on thermal performance, building energy, and precinct microclimate

Article References: Tong, S., Zhang, S., Ang, Y. Q., Ignatius, M., Xu, R., Lim, J., Oo, M. L., Tan, E., & Wong, N. H. (2026). Multi-scale evaluation of cool façade paints for tropical built environments: real-world impacts on thermal performance, building energy, and precinct microclimate. Results in Engineering, 32, Article 112782. https://doi.org/10.1016/j.rineng.2026.112782

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.112782

Keywords: cool paints, solar-reflective coatings, urban heat island, building energy efficiency, façade retrofit, tropical climate, difference-in-differences, microclimate monitoring, cooling load reduction, thermal comfort, Singapore, decarbonization

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Sloane Callahan. (September 8, 2026). Cool façade paints cut heat, energy use, and microclimate warming in tropics. Scienmag. https://scienmag.com/cool-facade-paints-cut-heat-energy-use-and-microclimate-warming-in-tropics/

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