“To block heat exchange, you can put a lot of insulation in your walls, but windows need to be transparent,” said Ivan Smalyukh, a materials physicist at CU Boulder and senior author of the research. “Finding insulators that are transparent is really challenging,” he added.

The material, called Mesoporous Optically Clear Heat Insulator, or MOCHI for short, is a silicone-based gel that traps air inside an intricate network of microscopic pores. The research team described the invention in a study published in Science on December 11. In its final form, MOCHI is more than 90 per cent air, which is the reason behind its impressive insulating ability.

The idea draws inspiration from aerogels, lightweight insulating materials already used in demanding environments such as NASA’s Mars rovers, where they protect sensitive electronics from extreme cold. Like aerogels, MOCHI relies on trapped air to block heat flow. But the crucial difference lies in structure. Aerogels typically contain randomly distributed air pockets that scatter light, giving them a cloudy appearance often described as “frozen smoke.” MOCHI, by contrast, is engineered to remain almost perfectly clear.

The researchers achieved this by carefully controlling how air pockets form inside the material. During production, they mix surfactant molecules into a liquid silicone solution. Much like oil separating from vinegar in salad dressing, the surfactants naturally gather into thin, thread-like structures. Silicone molecules then coat the outside of those threads. In later steps, the surfactants are removed and replaced with air, leaving behind what Smalyukh vividly described as a “plumber’s nightmare” of microscopic pipes running through the material.

Those pipes are many times thinner than a human hair, and their tiny size is what makes MOCHI such an effective barrier to heat. In gases, heat normally travels when energised molecules collide with one another. Inside MOCHI, the air-filled pores are so small that those collisions are disrupted.

“The molecules don’t have a chance to collide freely with each other and exchange energy,” Smalyukh explained. “Instead, they bump into the walls of the pores.”

The result is striking performance. A sheet of MOCHI just 5 millimetres thick is enough to shield a person’s palm from the heat of an open flame. At the same time, the material reflects only about 0.2 per cent of incoming light, meaning it remains nearly invisible when applied to glass.

The team envisions MOCHI being produced as thin sheets or larger slabs that could be fitted onto the inside of existing windows. Because it is long-lasting and highly transparent, it would not distort views or darken rooms, unlike many insulating films currently on the market.

“No matter what the temperatures are outside, we want people to be able to have comfortable temperatures inside without having to waste energy,” said Smalyukh, who is also a fellow at CU Boulder’s Renewable and Sustainable Energy Institute.

Beyond improving comfort, the researchers see potential for MOCHI in energy-harvesting applications. Because it allows sunlight to pass through while trapping heat, the material could form part of systems designed to collect solar warmth and reuse it inside buildings.

“Even when it’s a somewhat cloudy day, you could still harness a lot of energy and then use it to heat your water and your building interior,” Smalyukh said.

For now, MOCHI remains a laboratory-made material. Producing it currently involves time-consuming and labour-intensive steps, and it is not yet available for commercial use. However, the researchers note that the raw ingredients themselves are relatively inexpensive. With further work, they believe the manufacturing process could be streamlined enough to make the material practical for everyday architecture.

If that happens, future windows may look no different from today’s—while quietly behaving like a layer of invisible, high-tech bubble wrap, keeping buildings warmer, cooler and far more energy-efficient.