Rahul SomvanshiA recent Bloomberg Opinion report and accompanying video from columnist Lara Williams has put a decades-old piece of physics back in the spotlight: paints and coatings that cool buildings without consuming any electricity. Williams visited companies working on so-called radiative-cooling coatings and came away describing field comparisons that looked dramatic, which is what makes the underlying science worth explaining carefully rather than repeating as a single headline number.
Radiative cooling is not new chemistry. It combines two separate properties in one surface. The first is solar reflectance: the coating bounces most incoming sunlight, including the near-infrared portion that carries much of the sun’s heat, back into the sky instead of absorbing it. The second is thermal emissivity tuned to what scientists call the atmospheric window, a narrow band of mid-infrared wavelengths, roughly 8 to 13 microns, where Earth’s atmosphere is largely transparent. A surface engineered to emit strongly in that band can radiate its own heat straight past the atmosphere into the cold of space, rather than having that heat reabsorbed by water vapour and carbon dioxide overhead. A good radiative-cooling coating does both jobs at once: it rejects sunlight during the day and sheds heat continuously, day and night, through that infrared channel.
Bloomberg’s report centres on a handful of companies pursuing this approach commercially. Emissive, a London-based firm, has developed a coating it presents as capable of keeping treated surfaces markedly cooler than conventional paint under direct sun, based on its own demonstrations and the comparisons Williams observed on her visit. Solar Mantle, a US company working in the same space, is developing radiative-cooling materials aimed at roofs and other exposed building surfaces. AkzoNobel, one of the world’s largest paint and coatings manufacturers, is also named in the report as exploring reflective and heat-rejecting formulations at a scale that smaller specialists cannot easily match. Any specific figures tied to these companies, including claims of surfaces reaching around 20°C cooler than untreated materials or reflectance and emissivity figures near 95%, come from those companies’ own product demonstrations and the comparisons captured in Bloomberg’s reporting. They describe what was measured in those particular tests, not a fixed property of radiative-cooling paint as a category, and they should not be read as a guarantee of what any coating will achieve on a different roof, in a different climate, or at a different time of year.
That distinction matters most when moving from a surface reading to a building’s interior. A thermometer on a coated roof can show a genuinely lower temperature than an uncoated one nearby; infrared cameras make that difference easy to visualise. But the temperature of the air inside the building below depends on far more than the roof surface. Insulation, ventilation, window area and orientation, wall construction, internal heat sources, and whether the HVAC system is running all shape indoor conditions. A cooler roof reduces the heat load the building has to manage, which can lower cooling costs and ease the strain on air conditioning, but it does not translate on its own into a specific number of degrees cooler indoors. Two buildings with the same coating applied can see different indoor outcomes depending on how well they are otherwise built.
The practical case for radiative cooling rests on real, if more modest, benefits than a single dramatic figure suggests. Lower roof and wall surface temperatures mean less heat conducted into a building, which can meaningfully cut air-conditioning demand during peak heat, particularly in warehouses, data centres, and housing in hot climates where mechanical cooling is expensive or unreliable. At a city scale, widespread use of highly reflective, high-emissivity surfaces can contribute to reducing the urban heat island effect, where dense construction and dark materials trap heat that raises night-time temperatures across a neighbourhood. Coatings can also reduce thermal stress on roofing materials themselves, potentially extending their service life.
The constraints are just as real. Performance depends on a clear view of the sky; shaded, humid, or heavily polluted conditions reduce how effectively a surface can radiate heat through the atmospheric window, since water vapour and aerosols absorb some of the wavelengths the coating relies on. Dirt, dust, and weathering degrade reflectance and emissivity over time, meaning coatings need maintenance or reapplication to keep performing as tested. Orientation and roof pitch affect how much benefit any given installation sees, and the technology works on exterior surfaces exposed to the sky, not as a substitute for wall insulation or window glazing elsewhere in a building. Cost relative to conventional reflective or “cool roof” paints, which have existed for years, is also a factor in how quickly these newer formulations spread beyond demonstration projects.
None of that undercuts the genuine promise Williams’s reporting highlights. Passive cooling that works without electricity is valuable precisely because it does not add to the energy demand it is trying to reduce. The more useful next step is independent, climate-specific testing of these coatings on real buildings over full seasons, so that the benefits reported by companies like Emissive, Solar Mantle, and AkzoNobel can be verified outside their own demonstrations before they are treated as settled numbers.
