In 2024, NTU coated roofs, walls, and roads across a Singapore industrial block: afternoon air fell by 2°C, and pedestrians felt up to 1.5°C cooler outdoors

In 2024, a group of engineers in Singapore tested a solution to a problem many urban areas face: hot roadways and buildings that trap and store heat throughout the afternoon. The team created a coating to reflect sunlight and reduce heat absorption, and tested it on the roof, walls, and roadways of a single industrial block. They then left the neighboring industrial block alone as the control group and took temperature readings after two months. According to Nanyang Technological University (NTU), Singapore, afternoon air temperature at the experimental site was up to 2 degrees C cooler than at the uncoated counterpart. Pedestrians on the ground also felt up to 1.5 degrees C cooler.

Why the researchers tested a full city block

According to NTU, most previous studies on cool paint coatings have been simulation-based or tested in scaled-down models. Real-world environments are more complicated than any computer model or scaled replica can capture, so the NTU team wanted to test their theory on actual buildings. They found four buildings that formed a sort of two-building "street canyon" in an industrial park on the west side of Singapore. The team applied their specially treated reflective paint to the roofs, walls, and road surface of one canyon, leaving the other alone as a control. For two months, sensors measured temperature, humidity, radiant energy, and convection in the air between the buildings every day.


As a result, during the hottest time of day around 4 p.m., the painted side of the canyon emitted up to 30 percent less heat from its buildings than the unpainted side. Roofs with the paint reflected 50 percent more sunlight and retained about 40 percent less heat during peak hours than standard building materials. That should mean less heat is released back into the air later on, so the cooling effect lasts longer than just a few minutes after sunset.

What this means for hot US cities

According to the US Environmental Protection Agency, conventional pavement can reach surface temperatures of up to 152 degrees Fahrenheit at midday, while cool pavements remain 10 to 16 degrees cooler by reflecting more solar energy, enhancing water evaporation, or otherwise being modified to stay cooler than conventional pavement. According to the Centers for Disease Control, urban heat islands, aging infrastructure, and continued city growth are likely to increase the risk of heat-related illness for everyone in the coming years. Areas with more pavement and fewer trees are hotter than their surroundings, and that heat seeps into buildings, raising air conditioning costs and stressing the electrical grid at the hottest time of the year.

Why this works faster than infrastructure change

What makes the Singapore results interesting is not how much temperatures fell, but how easily they achieved the effect. Dr. E V S Kiran Kumar Donthu, who led the research in collaboration with NTU's Energy Research Institute, said cool coatings are a minimally invasive intervention that can provide immediate benefits, unlike major urban infrastructure changes that are costly and slow. Another advantage is reduced air-conditioning demand, because building surfaces retain less heat that must then be removed. As temperatures rise worldwide, practical solutions for existing infrastructure will be increasingly sought over large-scale projects that take years to plan and implement.

What researchers still need to test

The researchers also acknowledged that further studies should focus on the coatings' longevity and resistance to traffic, which makes sense, since any surface treatment is a fair investment only if it lasts long enough to justify the cost. However, questions remain about how well the approach would work in U.S. cities, where tree-planting and urban redesign take time to deliver results even as temperatures keep rising. And painting the tops of buildings or road surfaces with reflective coatings is a much faster solution than waiting for trees to grow.