Transparent wood: A better window than door

By Mariah Quintanilla

People have long used wood to build shelter, make furniture or stoke a campfire. The one thing we’ve never been able to do is see through it—until now. In two separate studies published this year, researchers from the University of Maryland and the KTH Royal Institute of Technology in Sweden devised a method to make wood transparent. They utilized similar techniques to chemically strip the wood of the compounds that give wood its color. The hope is to someday use the lightweight transparent wood as an energy-efficient alternative to traditional glass windows.

 Traditional glass windows are poor thermal insulators. The energy spent on regulating the temperature inside houses accounts for more than 50 percent of the total energy consumption in an average U.S. household, according to the U.S. Department of Energy.

“Wood has much lower thermal conductivity,” said Tian Li, a researcher on the University of Maryland study. “In terms of energy efficiency, it keeps a house at a more consistent temperature,” she said. This means heat stays inside a house in the winter and out in the summer.

To make the wood transparent, Li and her team first dissolve the lignin—the compound inside plant cell walls that makes wood brown and rigid. After they’ve bleached the wood using sodium hydroxide and hydrogen peroxide, only the cellulose-rich cell walls remain.

“Then it will become pure white,” said Li. At this point, the white wood is not yet see-through because the vertical channels that once transported water for the tree are not completely aligned.

So the team soaks the wood in an epoxy glaze. Once the epoxy infiltrates the vertical channels, the wood becomes clear and strong, essentially transforming the sheet of wood into a matrix of micro windows. The resulting wood “skeleton” is semi-transparent, yet stronger and more flexible than glass.

Researchers at the University of Maryland hold a pane of transparent wood over a leaf. (Photo by Tian Li)

“[About] 85 percent of light comes through,” said Li. She compared the transparent wood to frosted glass, or clear glass that has been sandblasted or acid etched. “It’s a little bit hazy, but if you hold the transparent wood right against something, you will be able to see the image quite clearly,” she said.

Tim Schultz, a glass retailer at South Shore Glass and Door in Tahoe, California is open to the idea of using transparent wood if it means making windows with better insulation than glass (better R-values). “If you get an R-value on transparent wood above an R-5, you would blow away anything you could do in the glass industry today,” said Schultz.

Glass windows that are triple-paned for more insulation are often too expensive and heavy. “The industry is hung up on the fact that there is only so much you can do with glass to make it energy efficient,” he added. Additionally, the transparent wood will not shatter like glass, and is completely waterproof.

The team also observed how well transparent wood might light up a room by replacing the roof of a birdhouse with the clear wood. When they shined a light inside the birdhouse, even at an angle, the inside of the birdhouse became illuminated by a uniform and comfortable light.

It may still be a few years before you can purchase a slab of transparent wood at your local Home Depot, but both research teams believe the idea of transparent wood will catch on rapidly. “We’re getting a lot of interest from architects, who want to bring more light into their buildings,” said Lars Berglund, a researcher at the KTH Royal Institute of Technology, in an interview with Fastco Design.

Meanwhile, you can make your own transparent wood by following this easy tutorial.

Photo at top: The transparent wood created by researchers at the University of Maryland has high impact energy absorption capabilities. (Photo by Tian Li)