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Bolt Threads’ Tannery Partner: ‘We’re Not Afraid Leather Will Disappear’

If Frank Fiedler, head of one of Germany’s oldest tanneries, feels threatened by the surging popularity of plant-based and fungal leather alternatives, he isn’t showing it.

“If these new materials are good, and the consumers accept them and want them, we will 100 percent support them,” Fielder, CEO of Heller Leder, told Sourcing Journal in an interview.

This isn’t merely lip service. The fifth-generation family-owned business has embarked on an exclusive partnership with Bolt Threads, the California startup whose ersatz cowhide has garnered the support of marquee brands such as Adidas, Lululemon and Stella McCartney. Bolt Threads makes Mylo by coaxing mycelium, the strand-like root network that sprouts mushrooms, to grow into organized mats of interconnected cells. Heller Leder then treats these sheets with natural tanning and other resource-efficient technologies, imbuing them with a more familiar pebble-like texture.

As Bolt Threads prepares to ramp up production by opening a new commercial-scale facility in the Netherlands that can pump out as much as a million square feet of Mylo, Heller Leder will be a critical partner, said Dan Widmaier, the materials firm’s founder and CEO. “Here’s a group that’s been practicing the art for a long time,” he said. “There’s a ton of knowledge about how to process leather hide into high-quality leathers for customers. We knew we should be tapping into that.”

For Fielder, it helps that Heller Leder’s other clients, such as Porsche and Rolf Benz are predominantly in the automotive and furnishing industries. Mylo is its first—and so far only—fashion product, which eases some of the tension that working with a vegan company might engender. “This is a good thing because it will not compete with the material from the other side of our company,” which sources 95 percent of its rawhides domestically, he added. “We can definitely concentrate on this interesting new material and stand 100 percent behind this partnership.”

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Fielder said that the partnership between Heller Leder and Bolt Threads is one based on “mutual respect and tolerance.” Both companies have agreed to “refrain from negative comparative advertising” of bovine leather and Mylo, presenting the latter instead as an “independent material” and natural alternative. “We’re not afraid that leather will disappear,” he said. “As long as humans eat meat, it’s a matter of fact that leather should be produced as good as it can be, as green it can be, and for long-lasting products. So we are convinced that both have the same right to exist.”

Mylo by Bolt Threads
Heller Leder and Bolt Threads have agreed to “refrain from negative comparative advertising” of bovine leather and Mylo, presenting the latter instead as an “independent material.”

Even with the European factory running at full tilt in 2022, Mylo will still be a sliver compared with the 35 billion square feet of cowhide that is produced every year, Widmaier said. He’s hopeful the company’s capacity will only keep growing, however. The accelerating interest in sustainable fashion has “been absurd” during the Covid-19 pandemic, driving demand for climate-sensitive novel materials like Mylo.

“That is just starting to scratch the surface, right?” he said. “I’m excited to send Frank so much that he can’t finish it all. So we’ve got a lot of work going on at Bolt to bring on this first factory, expand it and think about what we’re going to do after that.”

Even now, Bolt Threads has its hands full. Stella McCartney just feted a Mylo-clad version of its Frayme bag for its summer 2022 collection. Next year, Lululemon will offer yoga aficionados two bags that feature Mylo in their woven handles and braided pulls. In April, Adidas touted a proof-of-concept Stan Smith Mylo, though it didn’t state when the shoe will be available for sale.

Widmaier said he was impressed with how eagerly the so-called Mylo Consortium, which also includes luxury conglomerate Kering, embraced the material and began prototyping products. They’re “taking a new material into the world,” he said, “which is not what happens very often.”

“Materials development is historically a slow field—a very slow field,” Widmaier said. “I think that consumers have lacked the place to show tangible support for specific materials and products, and when our consortium partners go out there and do reveals or are starting to unveil them for launches in their collections, we’re seeing real feedback from consumers. Now, the angsty businessman in me wants to shoot a ton more product, but we’re working on that part.”

Indeed, if technological advances maintain their pace with consumer interest, annual sales of “low-complexity” leather alternatives made from plants, fungi and leather waste could soar past $1 billion by 2025, according to Lux Research, a Boston technology research firm. In a recent survey by the Material Innovation Institute, 80 percent of U.S. respondents were open to non-animal leather while 55 percent actively preferred “next-gen alternatives.” Enthusiasm for biomaterials was more fervent in China, where 90 percent of those polled said they preferred next-gen alternatives to the genuine article.

One thing that’s certain is that Mylo will continue to be a work in progress. The material is currently certified as 60 percent to 85 percent bio-based under the German DIN-Geprüft standard because it uses some petrochemicals in the finishing process. Bolt Threads plans to knock fossil fuels out of the equation altogether while staying “pragmatic” about potential trade-offs in performance.

“Everybody loves their polyurethane on the top,” Widmaier said, referring to criticism that plant- and fungal-based leather alternatives can contain a fair amount of plastic, belying their natural claims. “We hired somebody who came from another company working on biomaterials. And their first comment was, ‘Wow, you use a lot of biomaterial in this.’ We’re still not satisfied. We’re going to get it to 100 percent. That’s our roadmap.”