What if your house changed color with the seasons? This ‘climate-responsive’ paint could make it happen

When Joe Doucet bought a new house in Katonah, New York, he wanted to make it as environmentally friendly as possible. As a designer and inventor, he immediately found himself wondering whether the exterior of his home could play a role in mitigating the effects of climate change. “One of the things I had not really considered before was: What color should I paint the house?” he told CNN, speaking in a video call. It’s well known that light-colored buildings reflect heat and stay cooler while darker ones absorb — just compare chilly Scandinavia’s black housing tradition to the whitewashed homes found across warm Mediterranean countries. But what shade would perform best in a climate like New York’s, with hot summers but dark and snowy winters? Doucet started by 3D-printing small scale models of his house, complete with similar levels of insulation, and painting them in different colors. Over the course of a year, he found that in winter the inside temperature of the black model was on average 7 degrees Fahrenheit warmer than the white one. In summer, the white model house was 12 degrees Fahrenheit cooler. “The answer wasn’t, ‘Should I paint it black or white?’ The answer was: It should be black in winter and white in summer,” he said of the findings. “It is not really feasible to paint a house twice a year. I began to think, ‘Surely there are other ways of doing this?’” Doucet’s solution was inspired by his childhood interest in mood rings, which feature manmade “stones” that change appearance according to the wearer’s finger temperature. “I recall a fascination I had with a mood ring I received as a child and really trying to dig in and understand what it was,” he explained. “I knew, even as 7-year-old, that (the ring’s changing color) had nothing to do with my mood, that there was some type of chemistry at play. The chemistry that creates that change is very, very similar to what I used.” The process in question is called a thermochromic response, which refers to how chains of liquid crystals react to atmospheric temperature. In a mood ring, these liquid crystals are contained within the “gemstone,” causing its color to change. Doucet developed a kind of thermochromic pigment containing the crystals and started experimenting with a tin of ordinary housepaint and different additives. The result was a substance that could change color by absorbing ultra-violet light (which produces heat) above a certain temperature. Despite what he called the “great success” of his initial trials, Doucet found his new paints would slowly degrade in the sunlight. But after experimenting for another year, the designer solved the issue with the help of a protective additive. His climate-responsive paint, as he dubs it, appears “very, very dark gray” below 77 degrees Fahrenheit and gradually turns lighter as the temperature rises. Doucet has since filed a patent application for the technology. He admits his invention won’t be especially useful for people in consistently hot or cold climates. But Doucet believes his paint could be a “game changer” for those living in the world’s temperate zones — including large parts of North America, Europe and Asia — where average temperatures are typically higher than 50 degrees Fahrenheit in the warmest months but no lower than 26.6 degrees Fahrenheit in the coldest. Changing with the seasons Last year was the hottest year on record. It was also the first calendar year to breach 1.5 degrees Celsius above pre-industrial levels, a critical climate threshold. Doucet sees his invention as a direct response to this changing climate, rather than innovative new technology: “This could have been done 70 years ago, there was just no need for it,” he explained. “Climate change wasn’t an issue at the time.” But more than helping homeowners respond to rising temperatures, Doucet’s invention could have an impact on their climate pollution amid increasing energy costs and dependence on air conditioning (in 2020, 88% of US households used AC, up from 77% two decades ago). The operation of buildings accounts for 30% of global energy consumption, according to the International Energy Agency. But homes with improved thermal control consume less power by reducing demand for both air conditioning and heating. Doucet’s modeling “conservatively” predicts his paint could help households save between 15% to 30% on their energy costs. Beyond the science, Doucet believes there is beauty in the idea that buildings might shift with the seasons, like the leaves on a tree. “There’s something poetic about seeing the built environment and the built world change with the seasons in the way nature does,” he said. He also notes that new climate-responsive paints need not only change from white to black: “You can tint this pretty much any color,” he explained. A house could turn light blue in warmer months before turning a darker blue in the wintertime, he offered as an example. So, with his prototype technology developed, how long until people can paint their houses with it? “Five to 10 years,” said Doucet, caveating that its proliferation will depend on how people react to it. So far, he said, responses have ranged from “amazing” to “I don’t believe you.” The changing political climate may also impact his product’s route to market. President Donald Trump’s promise to “terminate” his predecessor Joe Biden’s clean energy policies — which he has called the “Green New Scam” — has created an uncertain climate for eco-investing. Doucet, who is also involved with an wind energy venture, says the resulting change in how investors respond to green projects has made him reluctant to raise venture capital and go at it alone. Instead, he hopes to find a partner that can bring the invention to market, like a paint company, a chemical company or some combination of both. “When situations change,” he said, referencing the Trump administration’s plans to cut subsidies and tax rebates for clean energy projects, “you need to change with them.” Nevertheless, Doucet appears confident that his creation has a potentially huge market. Not only could the paint be used on homes, but also larger buildings like schools, factories and other structures requiring a controlled internal environment. Though he is careful not to oversell the impact of his invention. “There is no single solution to climate change. It’s a series of steps and small actions,” he said. “But this could be a meaningful one.”