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Stanford Professor Yi Cui wears a prototype of the WarmLife jacket, which is designed to reduce energy use by keeping the wearer at a comfortable temperature.

Cui shows prototype CoolLife fabric, which is woven out of polyethylene, the same material as supermarket plastic bags.

Heating and cooling of buildings hogs energy. Cooling, the bigger consumer, accounts for about a fifth of U.S. energy usage, according to the U.S. Energy Information Administration — and that number is projected to rise rapidly as the world gets warmer.

Stanford Professor Yi Cui wants to slash that through “smart clothing” that keeps its wearers cool or warm, so they don’t have to crank up the thermostat or lower the A/C.

His Sunnyvale startup LifeLabs sells apparel that looks and functions just like regular sportswear but is made out of high-tech fabric he invented to regulate body temperature.

“We spend so much energy to do cooling during summertime and warming during wintertime to make people feel comfortable indoors,” said Cui, a professor of materials science and engineering at Stanford and director of its Precourt Institute for Energy. “If summer air-conditioning could go up 3 degrees Celsius, you could save roughly 30% of a building’s energy consumption. Every 1 degree Celsius saves 10%.”

The converse would be true in winter: save energy by turning down the thermostat if people’s garments could keep them warmer.

LifeLabs’ products include shirts, pants, shorts, windbreakers, jackets, vests, pants and pajamas, as well as bedding items like sheets and pillowcases. A short-sleeve button-up cooling shirt sells for $69 and a cooling windbreaker with SPF protection is $129, for instance.

But for apparel to significantly reduce energy used to heat and cool buildings, LifeLabs and similar products would need widespread adoption — by individual consumers, and more importantly, by corporate customers.

Imagine a factory, warehouse or school where everyone wore uniforms made from climate-controlled fabric. Those giant buildings could then rein in their energy usage. “If you could get a whole factory of workers to wear it, that could make a huge impact,” Cui said.

Backed by $13.8 million in venture funding, the 12-person LifeLabs has sold fewer than 10,000 garments since launching its direct-to-consumer sales last autumn. Cui acknowledges that it needs a lot more marketing to build awareness. It hopes to scale up by partnering with large garment makers and other commercial entities such as workplaces.

Using clothing to conserve energy hasn’t always been a popular concept. During the 1970s oil crisis, President Jimmy Carter was greeted with derision when he urged Americans to wear sweaters so they could turn down their thermostats.

But in the decades since then, attitudes have evolved as the pace of global warming has accelerated. Energy experts said any fast and cheap way to rein in energy usage has merit, compared to cumbersome solutions such as constructing new buildings.

“Getting customers to make small demand changes is a cost-effective way to reduce the need for additional grid hardware, whether it is more generation, more storage or more transmission,” wrote Severin Borenstein, a professor and faculty director of the Energy Institute at UC Berkeley’s Haas School of Business, in a blog post, albeit not specifically discussing apparel.

But Borenstein was dubious about the LifeLabs concept, saying in an email that social norms rather than tech clothing are what need to change. For instance, he said, “Japan declared a Hawaiian shirt summer after the Fukushima disaster and the associated electricity shortage they had the following summer. They turned thermostats to 82 degrees and it was considered a big success. Likewise, sweaters/sweatshirts and thick socks are a good way to stay warm in the winter.

“Bedding seems a more important breakthrough since there is lots of discussion of how to sleep cooler and the importance of sleeping in a cool room,” he said.

Donald Wulfinghoff, who runs the Energy Institute Press, which publishes guides on energy conservation, was even less enthusiastic about the concept.

“The claims about saving heating and cooling energy almost certainly fall under the category of ‘greenwashing,’” he wrote in an email.

But LifeLabs’ investors — who, of course, are not impartial — see it as a potential game changer.

“We strongly believe technology advancements will make a huge impact in the fight against climate crisis by empowering the individual to reduce personal energy usage,” said Bo Bai, founder of Asia Green Fund in a statement. In April his firm led a $6 million funding round into LifeLabs.

On a recent day, Cui wore a dark polo shirt and tan pants that appear indistinguishable from typical Silicon Valley apparel, both made from CooLife textiles. “You can feel the cooling right away,” he said, fingering his shirt.

He showed off a rack of LifeLabs items. Its WarmLife clothing traps human infrared radiation using a thin porous metallic coating that is sandwiched between regular textiles, he said. An entire jacket uses about as much aluminum as what’s in a paper clip, and is about a third lighter than a down jacket, Cui said.

“If you put your hands inside it, within 5 or 10 seconds you can feel the warmth build up; I feel it right away,” Cui said, demonstrating.

WarmLife is made from 97% recycled material, according to the company. Its nylon fiber is pre-consumer, such as left-over fabric cuttings and yarn waste, while its polyester is post-consumer, recycled from used bottles.

The CoolLife fabric is woven out of polyethylene, the same stuff as supermarket plastic bags. “CoolLife is made from a virgin thread as of now, with the goal to get to a recycled material in the future,” the company said.

Cui said its approach is superior to other cooling fabrics that use mesh weaves — essentially holes — to let body heat escape. “We do the cooling before the sweat is coming out,” he said. “I don’t think any other cooling technology can do that.”

The field of “climate clothing” is still so nascent that there are no independent studies to prove or disprove LifeLabs’ claims, and the company could not name any outside experts familiar with its work.

To be sure, there are rivals. Companies from Sony to Under Armour sell temperature-regulating clothing, and other university labs such as UC San Diego and the University of Maryland have announced breakthroughs in temperature-regulating fabrics. A quick Amazon search turns up more than 4,000 matches for “temperature control clothing.” Much of it is traditional items such as thermal underwear and moisture-wicking T-shirts; some is more edgy, such as heated electric underwear with Bluetooth controls.

LifeLabs tests its clothing using special mannequins that mimic human heat generation. The dummies’ temperature sensors show that CoolTech can lower body temperature by 2 or 3 degrees Celsius, Cui said.

Next on his drawing board is a bifunctional fabric that could both heat and cool as the temperature changes throughout the day. It’s not out yet but already has a name: DualLife.

“Any time you have a big temperature difference between day and night, or when you become hot when you run and cooler when you stay still would be useful for DualLife,” Cui said.

Carolyn Said is a San Francisco Chronicle staff writer. Email: csaid@sfchronicle.com Twitter: @csaid

Carolyn Said, an enterprise reporter for The San Francisco Chronicle, covers transformation: how society, business, culture, education and other institutions are changing. Her stories shed light on the human impact of sweeping trends. As a reporter at The Chronicle since 1997, she has also covered the on-demand industry, the foreclosure crisis, the dot-com rise and fall, the California energy crisis and the fallout from economic downturns.