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Flora or Fungi? Stella McCartney Won’t Play Favorites in Biomaterials Debate

When it comes to next-generation leather alternatives, Stella McCartney isn’t playing favorites.

At Paris Fashion Week on Monday, the British luxury house trotted out bags clad in Bolt Threads’ Mylo, which is grown from the root-like structures that sprout mushrooms, and Natural Fiber Welding’s Mirum, a customizable composite derived from plant-based waste such as cork powder, rice hulls and coconut fiber.

The use of both stems from Stella McCartney’s long-held philosophy of using no leather, fur, feathers or skins while “innovating cruelty-free alternatives that are kinder to our fellow creatures, people and Mother Earth,” the brand said.

Stella McCartney’s collaboration with Bolt Threads goes back years. The Frayme Mylo, the first mycelium-based high-end bag to trundle down a runway and become available for purchase, debuted at the same event in 2021. Monday’s brilliant white version marks the first time the ersatz leather has been commercially available in a color other than black.

“For years now, I have been so excited by Mylo and fungi’s potential to create a future of fashion free from the senseless murder of innocent animals for leather,” McCartney said. “The Frayme Mylo is the embodiment of that vision, with our new white edition allowing even more Stella women to have the luxury accessories they desire without compromising on their values.”

The bag’s “immediately recognizable” design, the rarified label said, includes a wraparound aluminum chain strap, a zero-waste zamac metal-alloy medallion, organic cotton rope and solvent-free Alter Suede made using pre-consumer recycled materials.

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Bolt Threads, a California-based materials-science firm, creates its spongy sheets of mycelial material in a vertical farming facility powered by 100 percent renewable electricity. The process starts by mixing fungal cells with sawdust and organic material. Under controlled temperature and humidity levels, filaments quickly spread upward and outward from the substrate to form a dense mesh. The resulting mats are then processed, embossed and finished by a gold-rated Leather Working Group tannery using Bluesign-approved dyes.

Because some petrochemicals are employed during this phase, Mylo is currently certified as 60 percent to 85 percent bio-based under the German DIN-Geprüft standard. The verified vegan material isn’t biodegradable, though Bolt Threads says it continues to work toward this goal. As a less environmentally damaging alternative to incumbent leather, however, Mylo works, the company said. Consider the 17,000 liters of water required to produce a kilogram of cowhide. Animal agriculture itself also accounts for roughly 14.5 percent of global greenhouse gas emissions.

“Stella McCartney and her incredibly talented team of thought leaders and designers have been at the forefront of championing sustainable materials like Mylo for years,” said Dan Widmaier, founder and CEO at Bolt Threads, noting the brand’s participation in the so-called Mylo consortium, which includes Adidas, Kering and Lululemon. “Our visionary partnership has inspired a materials innovation movement, paving the way for a more responsible fashion industry. It’s an honor to continue our long and storied relationship, and I am excited for everything we’ll collaborate on in the future—including this next major milestone of recreating the iconic Frayme Mylo in an exclusive new color.”

Stella McCartney Mirum bags
Models carry the Mirum-clad Falabella and Frame bags at Stella McCartney’s fall 2023 show at Paris Fashion Week. Courtesy

Stella McCartney’s partnership with NFW is a little newer. The Illinois-based company’s take on the Falabella and Frayme silhouettes is a plastic-free alternative to both animal and synthetic leathers that “still looks, feels, and performs like leather itself,” said Oihana Elizalde, vice president and manager of the Allbirds collaborator’s Mirum business unit. Together, the two companies worked to create not only the right dimension of suppleness but also a pebble grain never before seen in Mirum, which is both biodegradable and recyclable. A Global Organic Textile Standard-certified cotton fabric lines the interior.

Mirum requires no water during manufacturing or dyeing, NFW says. According to a recent life-cycle assessment, a square meter of the material generates between 0.8-2.1 kg of carbon dioxide equivalent from cradle to gate, or a fraction of the 110 kg of CO2e associated with cow-based leather and 7-15.8 kg of CO2e for polyurethane leather.

The Mirum-made purses are only a small part of a larger collaboration. NFW is a member of Stella McCartney’s Collab SOS Fund, a dedicated reserve that aims to provide “rapid, catalytic” capital to develop and scale-up climate solutions such as Mirum. Stella McCartney is also part of the firm’s efforts to grow “climate beneficial” and “farm forward” cotton in California, with the goal of rebuilding soil carbon stocks, increasing the soil’s capacity to hold water and cutting out synthetic inputs. More is expected to come from this initiative soon.

“My winter 2023 show is both a celebration of the love between humans and animals, as well as a call-to-action to take a stand for our planet—the perfect setting to introduce my iconic Falabella and Frayme bags in Mirum,” McCartney said. “I have long dreamed of the day when we would see a plant-based alternative to leather that does not kill a single creature and can be easily given back to Mother Earth, without creating waste. There is no compromise on desirability or durability; the future of fashion has arrived.”

Is there room for more than one bio-based leather alternative? For Stella McCartney, all signs point to yes. The label joins Tory Burch, which last month released a version of its Ella tote in Modern Meadow’s BioFabbrica Bio-Tex faux skin. Gucci has developed its own substitute leather using a combination of viscose and wood pulp. So has Hermès with MycoWorks’ Fine Mycelium, whose properties now “rival cowhide leather” but is still “costly, limited, and extremely new to the market,” Lux Research analyst Tiffany Hua said. MarketsandMarkets Research estimates that the plant- and fungal-based leather market will reach $97 million by 2027.

“There is currently a large trend of material innovation happening, which in my opinion is a great thing,” Elizalde said. “All of these companies, such as [Bolt Threads], are working towards the same end goal as NFW and that is to leave the planet a better place. The discoveries made by our companies are breakthroughs that are reimagining the way the fashion industry will move forward.”

Eventually, all materials should eschew cruelty, harmful chemicals and plastics for a more planet-positive tack, she said.

“For the future of the sector, I envision a world that no longer has to rely on finite fossil fuels and linear plastics within the materials being used,” Elizalde said. “Our hope with this partnership is to inspire other fashion houses and beyond to adopt the regenerative practices used to develop materials like Mirum to promote responsible production and consumption.”