The roof of the Sydney Nanoscience Hub is white. Not like a freshly painted wall: it's pure white. A white that seems to absorb light rather than reflect it. Under the Australian sun, which beats down even in winter, the surface remains cold. Colder than the surrounding air. Much colder. Six degrees below ambient temperature, even with the sun at its highest. It's not magic, it's physics. And it's not just cooling: every morning, drops form on the experimental panels. Dew. Water condensed from the air. About 390 milliliters per square meter per day, on good days. A reflective paint that produces water. Eighteen months ago, it would have seemed like a joke.
How reflective paint that catches water works
The researchers ofUniversity of Sydney They have developed a nano-engineered coating that does two things at once. The first: it reflects 97% of solar radiation. The second: it actively radiates residual heat back into space through passive radiative cooling.The result is a surface that becomes cooler than its surroundings. Cold enough to cause water vapor to condense, just like what happens on a bathroom mirror after a shower.
Most commercial white paints use titanium dioxide as the main pigment to reflect UV rays. They reach a maximum of 80-90% reflectivity. That of Purdue University, which we talked about a few years ago, reached 98,1% using barium sulfate. This new Australian formulation takes a different approach: it uses structure instead of pigments.
The lining is made of polyvinylidene fluoride-co-hexafluoropropene (PVDF-HFP), a porous polymer. The microscopic air pores trapped in the material scatter sunlight in all directions without glare. No UV-absorbing chemicals that degrade over time. Just a physical structure that works.
Ming Chiu, technology manager of Dewpoint Innovations and first author of the study published in Advanced Functional Materials, explains:
"Our design achieves high reflectivity through its internal porous structure, ensuring durability without the environmental concerns of pigment-based coatings. By eliminating UV-absorbing materials, we overcome the traditional limitation of solar reflectivity by preventing glare through diffuse reflection."
Reflective paint, 6 months under the Australian sun
The team installed experimental panels on the roof of the Sydney Nanoscience Hub. Six months of continuous testing, with minute-by-minute data collection, were needed. The conditions were anything but mild: the Australian sun is among the strongest in the world. But the coating held up. No signs of degradation. No loss of performance.
Dew formed for 32% of the year. On optimal days, collection reached 390 milliliters per square meter. An average 12-square-meter residential roof could produce about 4,7 liters of water per day. A standard, larger Australian roof would hold 70 litres on a good day.
Droplets form on the surface and, thanks to a UV-resistant top coating, slide toward a collection point. A standard rainwater harvesting system can also capture condensation. In Sydney, with an average rainfall of about one meter per year, rainwater exceeds condensation by six times. But in arid areas, the equation changes considerably.
But does it also work in the desert?
Chiara Neto, professor at theUniversity of Sydney and head of research, dispels a myth:
While humid conditions are ideal, dew can also form in arid and semi-arid regions where nighttime humidity increases. It's not about replacing rainfall, but about supplementing it: providing water where and when other sources become limited.
It's like a passive dehumidifier. At night, relative humidity rises, even in the desert. The cold surface of the roof attracts vapor and condenses it. It's not water in industrial quantities, but for high-value horticulture, for misting systems for cooling, or even for hydrogen production (which requires about nine liters of water per kilogram), it could make a difference.
Reflective paint, from the lab to the paint roller
The prototype tested in Sydney, as mentioned, uses PVDF-HFP, a material with some environmental problems. But Dewpoint Innovations, the startup that obtained the license from the university in 2022, is developing a water-based formulation with similar performance. It can be applied with standard rollers or sprayers. The price is comparable to a standard premium paint.
Perzaan MehtaCEO Dewpoint Innovations, He says:
"We are proud to collaborate with the University of Sydney to bring this breakthrough in passive atmospheric water harvesting through paint-like coatings. It's a scalable, zero-energy solution that transforms rooftops and remote infrastructure into reliable sources of clean water."
Commercialization is expected before 2030, according to Sebastian Pfautsch of Western Sydney University, who was not involved in the research but is closely following these developments. The market for "cool roof" coatings is growing, and this technology adds a concrete advantage: not only less heat, but also additional water.
Roofs that not only protect, but produce
Urban roofs absorb heat and contribute to the “urban heat island” effect, which can raise city temperatures by 1-13°C compared to rural areas. A cladding like this not only cools the building underneath, but reduces the city's overall thermal footprint. In well-insulated buildings, the effect on upper floors might be more limited. But in most Australian homes, where insulation is poor, the benefit would be immediate.
And then there's the water. Not a lot, but constant. Predictable. Collectible even when it doesn't rain. In a world where water scarcity is becoming an increasingly serious problem, every liter counts. Professor Neto concludes: "Imagine roofs that not only stay cooler, but also produce fresh water. That's the promise of this technology."
It's not the definitive solution to the climate crisis or drought. But it's a concrete step forward. A roof that works for you instead of heating your home. A type of multitasking that, perhaps, is worth considering.
