I’m holding a small square piece of what looks like leather. The front of the fabric feels like leather, soft and pebbled; it even smells slightly like leather. But the material, called Mylo, is made from mycelium, the root-like part of mushrooms. By the end of next year, for the first time, it will be produced at a commercial scale, in a facility that can make as much as a million square feet a year.
That’s still a very tiny fraction of the amount of leather made from animals. But it could be the start of a viable industry—one that can take on the environmental impact of leather or fake leather made from plastic. “When we look at leather, it’s a massive industry, like 35 billion square feet per year. And the net output of the alternatives rounds to about zero,” says Dan Widmaier, founder and CEO of Bolt Threads, the biotech materials startup that makes Mylo. “If we’re really going to make a dent in this problem that we call climate change, we better be able to go really fast.”
The company chose to work with mycelium in part because it was feasible to make in huge quantities. A large number of mushroom farms already exist—unlike, for example, the infrastructure needed to grow “lab-grown” leather from animal cells. In a very rough back-of-the-envelope calculation, Widmaier estimated that if all of the world’s current mushroom farms were converted to making mycelium for its leather, it would likely be possible to replace all of the leather on the planet. For now, as the startup grows, it’s working with mushroom farmers who want to diversify from food crops to make more money.
In the Netherlands, a global leader in mushroom farming, Bolt Threads partnered with a company that grows mycelium indoors in stacked trays. “The process is done in the dark in closed, climatically controlled chambers that replicate the conditions that this organism grows in, in the forest,” says Jamie Bainbridge, vice president of product development at Bolt Threads. “They’ve optimized those growing conditions around humidity, and light, and temperature—the basic things that we know it takes to grow this organism in very, very finely controlled conditions.”
The fungi grow on sawdust (waste from the wood industry), and the mycelium creates a fluffy white growth that looks a little like a large marshmallow in each tray. The harvested mycelium is processed in a series of proprietary steps that the startup won’t share publicly. Then the material goes to a tannery, just like regular leather does.
Some poorly run tanneries are a source of pollution. But the company partnered with one that carefully considers sustainability, and uses an approach that eliminates toxic chemicals like chromium. But the fact that the material is a fungus and not an animal hide also means that fewer chemicals are necessary. “The basic chemistry that is involved in taking a putrefying hide of a dead animal and turning it into something that won’t rot—you can just imagine what has to be done to make that happen,” says Bainbridge. “There’s this notion with consumers that leather is a natural material. Leather is actually about 40% chemistry and 60% animal hide.” Mycelium doesn’t rot, and doesn’t need to be preserved in the same way.
The bigger sustainability benefit of the material comes from the fact that it isn’t made from a cow. Bolt Threads doesn’t plan to release specific numbers about the CO2 savings and other benefits of mushroom leather until the material is coming out of the factory at scale, and it’s possible to accurately measure those figures. But the company has used lifecycle analysis “to see where hotspots are in our process,” and where they can be improved, Bainbridge says. And the basic facts suggest that the benefit will be large. “Growing a cow takes one to two years,” she says. “It takes growing the feed before you grow the cow. And so you’ve got a huge impact embedded in that cow. Mylo takes less than two weeks to grow.” Using mushrooms also avoids the ethical problems of killing an animal, though leather is typically a byproduct of the meat industry, from animals that were already killed for food. (The new material may have the most environmental impact if meat and dairy consumption also steeply decline.)
The company has produced, so far, more than 5,000 iterations of the material. The current version, finished and embossed like traditional leather, is uncannily like the real thing. “When I hand a person a piece of material, if they keep holding that material while we’re talking and sort of moving it around in their hands, subconsciously, they’re trying to figure out what they’re holding,” she says. And you see people do this over and over again with Mylo. They don’t put it back down on the table.” It has a natural feel, she says, unlike a vegan leather made from plastic.
For the last few years, the startup has worked with four brands—Adidas, Lululemon, Kering, and Stella McCartney—to develop the material, with Bolt Threads sending sample after sample for feedback. The brands have innovated themselves; when Lululemon wanted to develop a prototype yoga mat, and Bolt Threads didn’t know how to solve the challenge of making the material large enough, Lululemon’s designers created a woven pattern. Next year, the brand will release two bags made with the material, and Adidas will release a Stan Smith concept sneaker. While the leather will eventually come in many different forms, this first version is more limited. “They can have any color they want, as long as it’s black right now,” says Bainbridge.
The first products are still a small step. “But it means we’ve scaled the production of mycelium, it means we’ve put the processing in place, it means we have the tanning partnerships in place, and it means we have the customers to buy it,” says Widmaier. “It’s not a pair of shoes on everybody’s feet—it doesn’t get that far. But it gets you much further in products being out there for consumers to buy, interact with over time. Our burden to bear is to make that number way bigger, as fast as we can, to serve the many customers who want access to Mylo and sustainable material alternatives.”