Editing and story by Alix Hines

Video shot by Jason Zucker and Allbirds

NEW YORK (Circa) — Shoes are a part of our everyday routine, but have you ever stopped to think about the materials they’re made from?

The shoe startup, Allbirds, certainly has, and they’re “branching out” from their original line of Merino wool kicks.

On Thursday, Allbirds launched the Tree Collection, which is a sustainable line of shoes crafted using eucalyptus fibers.

“It starts with wood pulp, and we take our wood pulp from eucalyptus trees harvested in South Africa,” explained Joey Zwillinger, an engineer and co-founder of Allbirds. “They’ve done [this] with no irrigation, with the most sustainable practices, and we actually got a Forest Stewardship Council certification, FSC, on top of this fiber because of how sustainable it is and how effective it is in sucking carbon out of the atmosphere.”

The certification means the materials used to make this line were sourced in a way that protects both the forest and the animals that live in it.

Zwillinger added that this is the first time the upper portion of a shoe has been FSC certified.

“They’ve done a couple with some rubbers for the bottom, natural rubbers, but never with an upper, so this is a pretty big first for the industry,” he added.

Tim Brown, the co-founder of Allbirds and a former New Zealand World Cup soccer player, said the Tree Collection grew out of feedback the startup received from their customers.

“What we were finding was that it was a sub-optimal experience when the weather got really really warm,” he said.

So Brown and Zwillinger set out to develop a more breathable material for that would meet their customers’ needs in the summer months.

“We really wanted to create something that could really meet that comfort experience and those needs, and eucalyptus fiber has this amazing cooling sensation when you touch it, which was an amazing start for us, but not the full story,” Zwillinger said.

From there, Zwillinger said they took a long time to figure out how to knit the fiber. Ultimately, they ended up creating a shoe with more airflow and were able to still incorporate their signature Merino wool into certain areas of the insoles for extra comfort.

In addition to exploring a new material, Brown said Allbirds is also adding a third style, the skipper. So now in addition to their original wool runners and wool loungers, customers can also choose from the tree runners and tree skippers.

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Brown said although Allbirds, which launched in 2016, is a shoe company, at its core, he sees it as a “sustainable material innovation company.”

“Sustainability is not something to be proud of,” Brown said. “It’s something that everyone should be doing in the context of making things and that’s what we’ve tried to do from the very foundation of this company.”

That’s why instead of using synthetics, like many footwear companies, Allbirds started with wool. And Brown said the company plans to continue looking for innovative materials to meet the needs of their customers.

“”We believe there’s a lot of other opportunities for materials to be introduced into the footwear space that aren’t currently used,” Brown said. “We also think that there’s other problems that we know to solve for our community of people, other comfort problems, like when it rains or when it snows, so there’s a pipeline of innovation that we’re really, really excited about.”

Read more stories from Alix Hines on Circa.