A cement-based paint that "sweats" water kept a model house more than 4.5°C cooler than conventional white paint

If you have ever touched a sun-baked wall and pulled your hand away, you know why this matters. A team at Singapore’s Nanyang Technological University (NTU) has created a paint that cools by absorbing and evaporating moisture. A model house painted with this new paint was more than 4.5°C cooler than the same house painted with conventional white paint, without consuming a single unit of electricity, according to the study titled ‘Passive cooling paint enabled by rational design of thermal-optical and mass transfer properties’ published in Science on June 5, 2025.

Why conventional cooling paints struggle

Most cooling paints perform one of two functions: they reflect sunlight like a mirror, or they radiate heat into the sky as infrared radiation, a process called radiative cooling. Both work best in dry weather. But Science News reports that in humid places, moisture in the air traps that escaping heat near the surface, so the wall is warm anyway, and that gap is what the NTU team set out to fill.


How does a paint actually sweat?

The human body stays cool when sweat evaporates from the skin, carrying heat away. The paint works on a similar principle. The scientists at NTU were inspired by this and used cement to develop their cooling paint. The paint, called CCP-30, contains a porous gel-based material made of calcium silicate hydrate, a cement-like compound. In this structure, water is trapped in small pores like a sponge, and as it evaporates, it carries heat away from the wall. The paint combines three cooling mechanisms. It reflects sunlight, emits heat as infrared radiation, and cools by evaporating water. As Associate Professor Hong Li, the lead material scientist in the development of the paint, puts it, passive cooling was the main inspiration because ordinary cooling paint cannot cool effectively once it is trapped by moisture.

The numbers behind the claim

According to Science News, the paint reflects about 88% to 92% of sunlight and emits nearly 95% of absorbed energy as infrared radiation, even when wet. It can also hold water equal to about 30 percent of its own weight. CCP-30 offers almost 10 times more cooling power than commercial cooling paints under tropical conditions, according to the study, which reduced electricity consumption for air conditioning by approximately 30 to 40 percent in pilot tests. For the test, scientists painted three small model houses in Singapore with different coatings: white paint, a commercial cooling paint and CCP-30. All three models were left outside for two years in Singapore’s weather, including rain and humidity. The house painted with the new paint remained the coolest, being almost 4.5°C cooler than the other two, the researchers reported.

Why it doesn't fade like other cooling paints

By the end of the two years, however, the two other paints were noticeably yellowed and thus would reflect less light from the sun. CCP-30 was still white, Jipeng Fei, a co-author of the paper, told Science News. He attributed the result to nanoparticles in the paint, which help preserve its reflective and mechanical properties over time. Some polymers and salts help keep the paint crack-free and moist.

Why the rain doesn't wash it out

A water-based coating can dry out, which is an obvious challenge. The researchers implemented a fix. The paint absorbs rainwater and moisture from the air, allowing it to keep evaporating and cooling during long cloudy or rainy periods. PhD student Fei Jipeng added in comments to the university that the paint traps moisture when it rains and boosts its cooling power when the sun comes back out.

Why the research matters

Space cooling currently accounts for almost one-fifth of the total electricity consumption in buildings globally, but this figure might keep rising since summers are becoming progressively hotter. In humid, densely built cities where roof temperatures can rise sharply, and reflective paints lose effectiveness, this paint could be worth considering. The paint could also help reduce the urban heat island effect in cities such as Singapore, São Paulo and Los Angeles.

Don't expect it at your local hardware store yet

Before planning a renovation around it, keep in mind that this is still early-stage technology, tested on small model homes, not on full residential buildings at scale. The NTU team has reportedly spun off a company to commercialize the technology. No official word has been given on pricing or global availability yet. It is also worth noting that CCP-30 is a different product than another NTU cool paint, a reflective-only coating that Singapore’s Housing & Development Board has already committed to rolling out across all existing public housing estates by 2030, which shows the traction this category of technology is gaining, even if CCP-30 itself hasn’t gotten to that stage yet.

A paint that mimics human skin, reduces electricity use, and lasts two years in tropical weather without yellowing could have practical value. With temperatures on the rise, low-energy solutions like these may become just as important as the air conditioners we can’t live without today.