February 1, 2026 | By Scott Jenkins
Buildings lose considerable heating and cooling energy through their windows, so window coatings with low thermal conductivity would improve efficiency. However, finding insulating materials that are also transparent is a challenge. A team of researchers at the University of Colorado at Boulder (www.colorado.edu) has developed a novel insulating material for windows that lowers thermal conductivity, but that also allows visible light to pass.
The material, called mesoporous optically clear heat insulator (MOCHI), has been made in large slabs (>3 cm thick) and in thin sheets a square meter in size that can be applied to the inside of a window (photo). MOCHI is a relative of aerogels — synthetic materials that are interconnected nanostructures with very high porosity and low density. While aerogels have good insulating properties, their structure reflects light, making them ineffective for windows. On the other hand, the pockets of air trapped within the MOCHI structure are precisely controlled in such a way that light in the visible wavelength range is able to pass through.
To make the material, the research team used a solution-based process in which methyl trimethoxy silane (MTMS) is added to an aqueous solution of specially selected surfactant molecules. Addition of acetic acid and tetramethyl ethylene diamine form a crosslinked network of polysiloxane hydrogel, which contains the surfactant molecules. A subsequent solvent-exchange process with ethanol washes out the surfactant molecules. Because of the way the surfactants self-assemble in solution, the material is left with highly ordered networks of air pockets making up 90% of the material’s volume.
The network of air bubbles in MOCHI are of a size and shape that prevents heat exchange, while allowing greater than 99% of visible light to pass. Ivan Smalyukh, senior author of the study and a professor of physics at CU Boulder, explains: “Because the pores were much smaller than the mean free path between collisions of air molecules at ambient temperatures and pressures (60 to 70 nm), these molecules collide with the pore walls more often than with each other, so gas conduction of nanoconfined air was strongly inhibited.”
“The tubular polysiloxane network of MOCHI was also a poor thermal conductor because of its geometric complexity, poor thermal contacts at tubular junctions and small solid fraction by volume,” he continues.
Researchers envision the material as window insulation, preventing heating and cooling loss in buildings, or as a heat-trapping device to harness sunlight for energy for water-heating, for example. The research appeared last month in the journal Science. The researchers are now streamlining the process for making MOCHI, which uses inexpensive materials but is currently time-consuming.