Berkeley Lab (US) has developed a roof coating that keeps a building warmer or cooler, depending on the weather. Other reflective surfaces like super white paint work well to keep your house cool in summer, but they also keep it cooler in winter. This new material is called a temperature-adaptive radiative coating (TARC). When it’s warm outside this material reflects heat to cool the building, but in colder weather it automatically switches to trapping heat so that the building stays warmer. This reduces energy use and expense for both heating and cooling. 





TARC absorbs heat from the sun, but when the ambient temperature is above 30 degrees it sends 90% of the heat back to the sky. However, when the temperature outside is below 15 degrees, TARC emits just 20% of its heat, with 80% staying on the building. What makes this work is a strange compound called vanadium dioxide (VO2). When the weather is cool this material allows heat from the sun to pass through it to warm the building. The researchers say that TARC would save at least 10% on the cost of electricity for the average home. It could also be adapted to regulate temperature for cars, electronics, and satellites.