Chemistry, Materials & Packaging
New Insulating Paints Reduce Energy, Costs, Emissions, Discomfort in Extreme Temperatures

Stanford University scientists have developed a new kind of paint that can keep homes and other buildings cooler in the summer and warmer in the winter — significantly reducing energy use, costs and greenhouse gas emissions (GHGs).

According to the International Energy Agency, using air conditioners and electric fans to keep buildings cool accounts for nearly 20 percent of the total electricity used in buildings around the world; while space and water heating account for almost half. The Stanford researchers say the two combined account for roughly 13 percent of global energy use and about 11 percent of GHGs. In a study published today in Proceedings of the National Academy of Sciences, the researchers say their new paints reduce the energy used for heating by about 36 percent in experiments using artificial, cold environments; and reduced energy needed for cooling by almost 21 percent in artificial warm conditions. In simulations of a typical mid-rise apartment building in different climate zones across the US with the new paint on exterior walls and roofs, total heating, ventilation and air-conditioning energy use declined 7.4 percent over the course of a year.

“Energy and emissions from heating are forecast to continue to fall due to energy-efficiency gains; but air conditioning use is rising — especially in developing economies in a warming world,” said the study’s senior author, Yi Cui — professor of materials science and engineering, of energy science and engineering, and of photon science at SLAC National Accelerator Laboratory. “For both heating and air conditioning, we must reduce energy and emissions globally to meet our zero-emissions goals. How to reduce heat exchange between human living and workspaces and their surroundings is getting more attention, and new materials for enhanced insulation — like low-emissivity films for windows — are in demand.”

Underneath the colors

Objects of different materials in various shapes, coated with the new paints | Image credit: Yucan Peng

The infrared spectrum of sunlight, when it is absorbed by surfaces, causes 49 percent of natural heating on the planet. With 2023 on track to be the hottest year on record, the effects are being felt worldwide; and extreme heat can feel even hotter in cities, thanks to the heat island effect exacerbated by paved surfaces. Used in conjunction with solutions such as solar-reflective pavement coatings — which GAF is currently piloting in landlocked, overheated urban communities such as Los Angeles’ Pacoima neighborhood — Stanford’s new paints could be a game-changer for increasing the livability of buildings in a continually climate-changing world.

Low-emissivity paints tend to have a metallic silver or gray color — which limits their use, aesthetically. Stanford’s new paints are made of two layers — an infrared, reflective bottom layer using aluminum flakes; and an ultrathin, infrared, transparent upper layer using inorganic nanoparticles — which are applied separately and come in a variety of colors.

For keeping heat out, the new paints can be applied to exterior walls and roofs. Most solar infrared light passes through the color layer of the new paints, reflects off the lower layer, and passes back out as light — not being absorbed by the building materials as heat. To keep heat inside, the paints can be applied to interior walls.

The researchers say the new paints reflect up to about 80 percent of high mid-infrared light, which greatly increases the amount of heat kept inside during cold weather and outside during hot weather. The color layer also reflects some near-infrared light, reducing the need for air conditioning. The research team says their paints in white, blue, red, yellow, green, orange, purple and dark gray reflect high mid-infrared light 10 times better than conventional paints in the same colors.

Lightening the load for mobile refrigeration

The paints can also be used to improve energy efficiency in trucks and train cars used for refrigerated transportation — for which cooling costs can take up to half the transportation budget.

“Both layers can be sprayed onto assorted surfaces of various shapes and materials providing an extra thermal barrier in many different situations,” said Yucan Peng, co-lead author of the study and a postdoctoral scholar in Stanford’s Geballe Laboratory for Advanced Materials.

The researchers continue to evaluate the practicality and efficacy of their paints in various situations — including in extreme high and low temperatures, humid environments, etc — and to work on refining the paint formulations for various practical applications.

Read the study to learn more.