This paint acts like a dehumidifier for your walls

It looks like ordinary paint, but a new coating called Lilypad Paint has a hidden ability to pull moisture out of the air. It works like a dehumidifier, without the energy use.

If it’s on the wall in your bathroom, it can suck water vapor out of the air after you’ve taken a shower. The paint holds the humidity in nano-size pores, and then slowly releases it as humidity levels fall in the room. Under the paint, a layer of custom primer “acts like a smart gatekeeper ensuring that vapor doesn’t end up accumulating in the wall,” says Derek Stein, founder and CEO of Adept Materials, the startup behind the product.

A passive fix for moisture in modern buildings

The tech spun out of Stein’s research as a physics professor at Brown University. While working with students on the design of a solar-powered house, he learned about a growing problem: As buildings become more energy-efficient, air quality can get worse.

“As we’re making buildings really, really tight thermally, they tend to trap in moisture and trap in air,” Stein says. A new house might use less energy for heating and cooling but more for ventilation—and if the system doesn’t work perfectly, the home could end up with mold. Older houses that don’t have mechanical ventilation also often have mold problems.

Stein iterated on new materials that could passively regulate humidity inside a building and landed on the idea of a simple two-layer structure. It’s “like a material machine that can regulate humidity in a space while also teaching direction to the wall,” he says. The design moves moisture out of the wall while preventing it from getting in.

In conversations with the construction industry, Stein realized there was a clear demand for a product like this. In 2018, he left Brown and launched the startup to bring it to market. “It became clear to me that to make this happen on any realistic time scale, I had to leave the ivory tower and go out into the proverbial real world to do this,” he says.

Scaling up outside the lab

The basic tech, which the company calls Vaporwisp, could be incorporated in many different building materials—drywall, for example, would benefit from humidity management. Adept Materials is also developing a new building wrap for construction that can keep moisture out without trapping it inside. In a seed round of funding a little over a year ago, investors included large home builders like D.R. Horton.

“Why are home builders investing in this? It’s not just because of the paint. A lot of their problems, operationally, are related to moisture,” says Stein. (The technology can also have broader applications, including packaging to keep food fresh longer, or moisture-wicking clothing.)

Paint was a logical place to start in part because it’s used both by builders and by consumers working on DIY projects. And unlike drywall—a low-margin, unbranded product—paint is something consumers can seek out by brand.

In hundreds of lab tests on the paint, the team showed that the system worked as expected to absorb and release moisture. In two identical rooms filled with humidity sensors, testers painted one with Lilypad and one with ordinary paint, and ran a series of humidity assessments. The new paint kept moisture out of the walls.

The process works as long as the paint is on the walls. In other words, the performance is tied to its physical properties, not to chemical additives that can wear out. “Lilypad works because it gives moisture a place to go, and a way back out,” Stein explains. “When humidity rises, water temporarily clings to tiny surfaces inside the paint. When the air dries, that moisture naturally releases back into the room. It’s the same everyday process that makes a bathroom mirror fog up and then clear again. The difference is scale: Inside a gallon of Lilypad, those invisible surfaces add up to about a million times the area of a mirror.”

After ensuring that the coating worked as expected on humidity, the company optimized it as a paint. The finish had to be perfect. It was engineered to flow onto walls as smoothly as top paint brands.

“We’ve really been engineering this to be a no-compromise paint,” Stein says. “The other thing, as a startup company, without the economies of scale that Sherwin-Williams and Benjamin Moore will have, we’re not going to be able to compete on price. And so we’re necessarily going to be competing with higher-end products. . . . We cannot be deficient in any of that.”

Because it’s being sold not just as a paint, but as a coating to control moisture, it’s sold at a premium: A kit with a gallon of primer and a gallon of paint goes for $175.

At launch, the coating is available only in white. “There’s a a kind of poorly kept secret within the paint industry that about 80% of paint sales are whites,” Stein says. “So people go into the paint store, they bring the pillows and a sample of the drapes and the whatever and they’re checking all the colors, and after an hour they go up to the front and they say, ‘A gallon of double white.’ We wanted to free people of the decision paralysis and free ourselves of the operational headaches of having to offer every color under the rainbow.” He notes that the company can easily add colors later.

Saving energy and money

In an ultra-tight new building like a passive house, the paint can’t replace mechanical ventilation. But it can reduce how much ventilation needs to be used, saving energy. “If you can automatically regulate humidity, it can lighten the load on the HVAC system—and that’s not insignificant,” Stein says. “The fraction of energy that goes to managing humidity in a building is typically . . . about 10% to about 40%.”

In an older building, Lilypad coating can reduce moisture without the need to install expensive new HVAC systems. Adept Materials is now in discussions with the Boston Housing Authority about a pilot that would test the paint inside public housing apartments that don’t have exhaust fans in bathrooms.

“It’s accessible by design,” Stein says. “My hope is that while we are releasing this and people are going to be putting it in fancy remodels, there’s also the opportunity to put it into public housing.”

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