Arbor Wood uses thermal modification for more durable products

One of Arbor Woods’ first major projects, completed in 2017, was the $79 million Bell Museum on the University of Minnesota St. Paul campus. 


Wood and water are not friends … at least not in a home. 

You know this whether you’re a DIYer or multimillion-dollar company building customized homes. Just think of wood finishes in basements that swell with humidity or the back-breaking joys of scraping and re-staining your deck.

Perhaps you’ve tried alternative finishes such as composite decking, committed to a lifetime of staining, or simply left your basement unfinished. Now, an alternative from a local business hoping to stake its claim in an eco-friendly process could change your options. Arbor Wood Co. in Duluth offers wood processed through thermal modification. In this process, wood is heated in an oxygen-free kiln, first dried to remove moisture, then “cooked” to induce chemical changes to the three primary cell components – lignin, cellulose and hemicellulose – in wood. The result is a product more durable, water-resistant and pest-resistant than the original wood. 

Thermal modification is not a new technology. Thermally modified wood production became popular in Finland in the late 1990s for sauna materials. This expanded to interior flooring, decking and siding. 

A primary driver of its popularity, in addition to its performance, is its eco-friendly alternative to chemically treated wood or non-renewable building supplies. The product became so popular that in the early 2000s that the Finnish government reached out to the University of Minnesota Duluth’s Natural Research Resources Institute (NRRI) to see if the institute could assist in marketing the product in the United States. NRRI’s work with thermally modified timber, including the new materials and the new plant processing knowhow, has garnered attention from Finish companies, mainly through national trade show booths educating trade professionals about the value of this technology.

NRRI has become a U.S. leader in research and development for the process and a resource for companies wanting to develop thermally modified wood production. In 2012, NRRI created one of the first pilot plants in the country to do additional research and development.

Around that time, owners of the Duluth-based Intectural, which distributes architectural materials with a commitment to conservation and sustainability, contracted with NRRI ultimately to aid with a start-up, Arbor Wood Co. For seven years, Arbor Wood has been mastering the thermally modified wood process and slowly scaling up production. Now the company is ready to expand.

According to CEO Jon Heyesen, Arbor Wood has partnered with investors from Voyageur Capital Group out of International Falls to create a new manufacturing operation. Voyageur purchased the abandoned Ainsworth plant in Grand Rapids and plans to reopen the space next spring. In it, Arbor Wood will install a state-of-the-art thermal modification kiln – just the second of its kind in North America – as well as a full finishing mill. 

“This is an exciting time for Arbor Wood,” Heyesen said. “We’ve just posted two key leadership positions for the plant including a plant manager and a process engineer.” Up to six line workers also will be hired. 

Matt Aro, wood products research program manager at NRRI, said the complex thermal-modification process at the plant will result in real benefits to the end user.

“It ultimately improves the wood,” Aro said. “As a result, it is more moisture resistant, dimensionally stable and rot resistant. In many ways, it behaves very similar to treated lumber, but without the chemicals. Another benefit is it creates a deep, rich color that can be similar to that of more expensive imported, tropical woods. That color is sought out in things like flooring that people pay a premium for right now.”

The two most common woods used by Arbor Wood Co. – yellow, or Ponderosa, pine and white ash – currently come from out of state. “One reason we use these woods,” said Heyesen, “in addition to their performance, is their rapid growth cycle. One key component of sustainability is how quickly wood can turn over.”

Wood grown regionally that responds well to thermal modification, such as white pine, tends to require longer growth time, but Heyessen said the hope is additional development will fine tuning of the process to make more species viable and more local woods useful. Arbor Wood Co. continues to partner with NRRI on research.

One of Arbor Woods’ first major projects, completed in 2017, was the $79 million Bell Museum on the University of Minnesota St. Paul campus. The project called for wood harvested within 250 miles of the building site for some exterior finishes. Ultimately, Arbor Wood supplied about 21,000 board feet of white pine from the Cass Lake area to cover nearly 40% of the building. Other projects followed, including at Epicurean’s new corporate headquarters in Superior, at Brooklyn Bridge Park in New York, at the National Air & Space Museum in Washington, D.C., and on high-end homes throughout North America.

Despite the benefits, the wood has been not widely used yet, in part because there are few suppliers undertaking the complex modification process. 

“The general availability is low for this product,” Aro said. “It is a niche product, with demand being driven by architects and designers on higher end building projects, but it isn’t readily available to the general consumer.”

With few outlets, thermally modified wood projects also lack a national association with a mission to promote it. Instead, individual players like Arbor Wood Co., work to market the product, educate consumers about its, and to be heard in a crowded building-supplies marketplace.

Lastly, as a newer niche product in the United States, national performance standards or quality rankings about products have yet to be established. Though individual companies warranty their products, having a governing body and regulations for a product can improve confidence of consumers, such as contractors, Aro and Heyesen agreed.

“There needs to be a change in U.S. building codes. As an industry, we’re starting to make headway in developing commercial standards, which will create better consistency, testing and, ultimately, adoption,” Heyessen said.

Arbor Wood Co. has seen an increase in calls from individuals looking for eco-friendly building alternatives. The company also has fielded calls from other markets, such as stand-up paddleboard and guitar manufacturers curious about whether thermally modified wood could be used in their industry.

Growth is projected for the thermally modified wood use. According to 360 Market Updates, the thermally modified wood market will see compound annual sales growth of 3.1% from $340.5 million in 2021 to $422.7 million in 2026.

Arbor Wood Co. hopes to capture a chunk of that growth. “We have a great product and name, along with unique partnerships to position us as the leader in the industry. Our hope is to have Arbor Wood become the Kleenex to modified wood,” Heyesen said. 

The company’s efforts appear to be paying off. From its modest start, sales revenue for Arbor Wood has increased nearly 600% in a year. 

The company has more than $10 million worth of pending contracts ranging from retail stores such as Lulelemon to hotels to national park projects. Arbor Wood Co. has also caught the attention of celebrity designers and industry influencers interested in using and promoting thermally modified woods.

“There really is no limit to how successful they can be,” Aro said of the new company. “We’re excited to continue working with them and to see how far they go.”

Beth Probst is a freelance writer based in Iron River, Wis.