'Bubble wrap' window coating could save huge amounts of energy worldwide

Windows are the Achilles’ heel of energy efficient buildings. You can stuff walls with insulation, but panes have to let light through, and most materials that trap heat also scatter it, turning your view cloudy.

That trade-off helps explain why buildings swallow roughly 40 percent of the world’s energy: they bleed heat on cold days and soak it up when it’s hot.

A team at the University of Colorado Boulder thinks they’ve found a way around the dilemma with a material that behaves like high-tech Bubble Wrap without the blur.

Clear insulation, wall-like performance

The researchers call the new material MOCHI, short for Mesoporous Optically Clear Heat Insulator. It’s a silicone-based gel that can be cast as slabs or thin films and applied to the inside of existing windows.

In early demos, a sheet just 5 millimeters (about 0.2 inches) thick was enough to let a researcher hold a flame over their palm without feeling the burn.

The trick is simple in concept and fiendishly elegant in execution. MOCHI fills more than 90 percent of its volume with tiny pockets of trapped air, yet remains almost perfectly transparent, reflecting only about 0.2 percent of incoming light.

“To block heat exchange, you can put a lot of insulation in your walls, but windows need to be transparent,” said physicist Ivan Smalyukh, the study’s senior author. “Finding insulators that are transparent is really challenging.”

Perfecting transparent bubbles

MOCHI is similar to aerogels – the ultralight “frozen smoke” NASA uses to insulate Mars rovers – but it solves a visibility problem that has long dogged those materials.

In conventional aerogels, pores form randomly and tend to scatter light, which makes them hazy. The CU Boulder team engineered the pore network from the ground up. They start with surfactants – detergent-like molecules – mixed into a liquid.

These self-assemble into hair-thin filaments, a bit like oil and vinegar separating. Silicone molecules in the same bath glom onto the outside of those threads.

Through a controlled swap, the researchers remove the surfactants and replace them with air. The process leaves behind a labyrinth of nanoscale “pipes” lined with silicone, a structure Smalyukh calls a “plumber’s nightmare.”

Windows block energy release

Heat slips through gases by molecular bumper cars: energized molecules smack into their neighbors and pass along energy.

In MOCHI’s microscopic channels, that game can’t get started. The pores are so small that gas molecules hit the walls more often than each other, dramatically reducing their ability to transfer heat.

“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.”

By tuning the pore sizes and silicone walls to minimize light scattering, the team keeps the material optically clear even as it throttles thermal flow.

From windows to solar energy harvesters

The most obvious application is retrofitting windows so homes and offices stay comfortable with less heating and cooling.

But the team also sees potential for passive solar devices that trap sunlight’s warmth and store it as low-cost heat even on days when the sky is milky rather than bright blue.

“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.

Because MOCHI works as a thin film, builders can laminate it onto glazing without bulky frames or tints.

Cost, durability, and scale

Right now, MOCHI is a lab-scale product rather than a hardware store roll. The process is time-intensive, and scaling it will take engineering work.

The good news: the ingredients are common and relatively inexpensive, and the structure is a silicone network – chemically stable, long-lived, and not prone to yellowing like some plastics.

The team is confident they can streamline manufacturing into a continuous process that produces large, uniform sheets for building retrofits and new construction.

“No matter what the temperatures are outside, we want people to be able to have comfortable temperatures inside without having to waste energy,” Smalyukh said.

Big energy savings ahead

Swap out a city’s leaky windows for panes coated in a film that’s nearly invisible yet strongly insulating, and the energy math changes. Heating loads drop in winter, cooling loads ease in summer, and peak demand flattens.

Because the performance comes from physics, not moving parts, the benefits accumulate quietly for years.

If manufacturers can produce MOCHI at scale and at a price competitive with conventional glazing upgrades, it offers a retrofit pathway that preserves daylight and views while cutting energy use.

There’s still work to do before MOCHI lands in storefronts and spec sheets. Researchers need to optimize the pore network for different climates, prove long-term durability in the field, and refine fabrication so it’s fast and repeatable.

But as a proof of concept, it’s compelling: a transparent, high-performance thermal barrier that lets windows be windows while helping buildings waste less.

The study is published in the journal Science.

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