Will Mycelium Save Cows’ Skin? Bolt Threads Is Working on it
In 2021, David Breslauer, co-founder and chief scientific officer at Bolt Threads, joined me on the Business for Good podcast to talk about his company’s advancements with non-animal, nature-based, bioengineered textiles.
In 2009, Bolt Threads was a student-led start-up hoping to score some government grants. A dozen years later, it has earned venture capital backing and more than $200 million in funding, in addition to partnerships with brands like Adidas and Stella McCartney. To date, Bolt Threads has raised more than $470 million (not a typo!) in funding.
From chemically identical spider silk created via fermentation to a mycelium-based alternative to leather, the science behind Bolt Threads has always focused on using innovation to drive sustainability and positive social and market change. In 2022, Bolt Threads earned widespread press for its Greener Pastures Pledge, in which it asked apparel brands to move away from virgin animal leather in exchange for priority access to Mylo, its high-quality leather alternative created from mycelium (the naturally fibrous roots of fungi).
Spinning the mysteries of silk
It all started with the spiders at the University of California, Berkeley. As a Cal student, David saw spiders crawling all over the campus and wondered how it was that they could spin fine threads of silk that were almost infinitely strong. He‘ ha’d always been fascinated by the properties of natural materials and held a commitment to sustainability, so he felt it was only natural that he was inspired to earn his PhD by focusing on research into methods for bioengineering spider silk. Part of his work involved looking at how nature is optimized for solutions and how biological and chemical materials can be manipulated.
To this day, David says, humans “barely understand” the mechanisms that allow a spider to spin its silk, an “almost magical” process. Spider silk is both strong and incredibly light, soft, and stretchy, with ultra-fine threads that are much stronger than the silk made by silkworms.
Fortunately, David met his counterpart across the Bay who was also interested in spider silk. At the University of California, San Francisco, Dan Widmaier was studying how best to provide optimum conditions for growing things. Dan went on to earn his PhD in chemistry and chemical biology by researching how genetic circuits could be used to control microbial organelles.
After the two researchers saw how mutually beneficial their interests were, the idea for Bolt Threads was born. Back in 2009, small business innovation government grants were the typical way of funding for young entrepreneurs pioneering new technologies. David and Dan won all four of the government grants they applied for, finished their doctoral theses, and spent the next year working out their ideas until they also began to secure VC funding. Foundation Capital was the first to see the potential in their spider silk project.
Bolt Threads introduced its protein-engineered spider-silk fibers in 2012. In 2017, the company was producing spider-silk ties, along with its Microsilk brand fiber. It collaborated with Stella McCartney, who fashioned a gold silk dress from the company’s spider silk, and introduced its b-silk protein product and Mylo alternative leather in 2018.
Making a leather-like material out of mushrooms
After building a consortium of well-known apparel brands committed to furthering the exploration and development of Mylo as an apparel material, Bolt Threads introduced products branded by Adidas, Stella McCartney, and Lululemon in 2021. In 2022, Bolt Threads announced new partnerships with GANNI and Tsuchiya Kaban.
Their knowledge of materials science caused David and Dan to wonder what else they could create in terms of advanced apparel applications. For example, could they develop Kevlar-like vests made from engineered natural fibers that wouldn’t melt in intense heat the same way polymer-based clothing does?
After working with outdoor apparel makers like Patagonia, they wanted to develop fabrics that would go beyond the utilitarian to the luxurious, which lead them to Stella McCartney.
As they worked to use quick-growing mycelium as a leather alternative, that part of their business began to take off, too. Dan and David had realized that mycelium, grown in layers, offers a protein analogous to that found in animal leather.
In addition to concerns about animal cruelty, traditional animal leather operations are highly unsustainable and contribute an outsized share of greenhouse gas emissions. All Bolt Threads’ lines of research and development center on this commitment to animal welfare and sustainability.
The spider silk and mycelium leather processes both rely on fermentation, but on dramatically different kinds. Bolt Threads’ spider silk manufacturing involves liquid fermentation — growing microbes in a vat. Its production of mycelium leather involves solid-state fermentation, where the fungus is grown on materials like sawdust. In the end, it’s all fermentation. You get the feedstock, sterilize it, grow the microbes, purify the output, and form it into the material.
All along, Bolt Threads has excelled at prototyping biological materials and integrating its products into textiles. Working closely with McCartney and other designers has given the company the ability to move beyond producing materials using merely quantitative scientific data and into the area of artistic expertise that’s much more difficult to quantify. What are the attributes of a textile? Does it age and drape well? What is its “hand,” the way it feels against the skin?
Innovation in design and manufacture
Bolt Threads is working to reverse-engineer the final product that discerning consumers want in their leather goods. Since mycelium is a fungus, the company has to deactivate its capacity to grow while ensuring quality control to produce the desired look and feel. Bolt Threads precision-cuts the sheets of mycelium and includes custom features, like embossing, found in animal leather. But, as David explains, all this is less of a chore than the chemical processing, grading, and manipulation of animal hides used to produce traditional leather.
Based in the Bay Area, Bolt Threads operates most of its enterprises in Europe, close to the facilities that have the equipment and the traditional expert knowledge of leather processing that it needs. This also places the company close to the headquarters of the major brands in the consortium it works with. David and Dan run a dedicated growth facility where they produce the sheets of mycelium under standards focused on sustainability and worker rights.
The podcast is as riveting today as it was when we recorded it, so go take a listen. I think you’ll appreciate Bolt’s work as much as I do.
