H&M is doing it. Levi’s is doing it. Even Zara wants a seat at the table. In fact, a total of 64 companies representing 143 brands and a combined value of 7.5% of the global apparel market have thrown their support behind a transition to a circular fashion economy, where products are made to be repurposed and recycled, rather than tossed into a landfill at the end of their useful lives.
But while the scientists of the world are close to cracking the code of spinning new clothing from old, finding circular solutions for footwear is proving to be a greater cipher.
The problem lies with the way shoes are constructed. Shoe manufacturing is a complex endeavor, perhaps even more so than most apparel. A typical athletic sneaker, for instance, can comprise dozens of materials—leather, foam, textiles, metal, rubber, wood—all of which are difficult, if not downright impossible, to tease apart after they’ve been glued or stitched together. This is generally a good thing: you don’t want your shoe to fall apart while you’re pounding the pavement, after all. But it doesn’t bode well for end-of-life disposal.
“All those different materials and parts, which serve different functions, are composed in a way that really have a difficult time being separated,” said Annie Gullingsrud, director of textiles and apparel at the Cradle to Cradle Products Innovation Institute. “And basically even if a collections and sorting facility gets them, in most cases they’re going to end up being trashed.”
The volume of footwear that winds up in the landfill can certainly add up. While solid data for footwear production and disposal can be hard to come by, Shahin Rahimifard, director of Loughborough University’s Centre for Sustainable Manufacturing and Recycling Technologies (SMART), estimates that some 20 billion pairs of shoes are manufactured every year.
Shoes tend to have a brief shelf life, as well. A 2011 survey found that most women will wear a pair of shoes for an average of three years before giving them the boot.
“Looking at the patterns of lifestyle, how long people keep their shoes, and lots of other research that we’ve done, we believe around eight to 10 billion shoes come to end of their life— almost half of what is annually produced—and that’s a very conservative estimate,” Rahimifard said.
Breaking it all down
For the past 10 years, Rahimifard has been studying what happens to shoes once they’re past their prime. In landfills, dyes and chemicals from tanned leathers, glues and other shoe components can leach into the soil and contaminate nearby groundwater.
After what Rahimifard described as a “long and challenging series of experiments,” Centre for SMART managed to design machines that crush shoes into fine granules that can be separated and reconstituted into new materials. The process is wholly mechanical—no chemicals are used or required.
SOEX, one of the world’s largest textile recyclers, is currently piloting a program based on Rahimifard and his team’s research. The firm receives about 35,000 used pairs of shoes—about 25 tons—every day at its footwear plant in Wolfen, Germany.
It’s a broader take on programs like Nike Grind, which pulverize used trainers—but only used trainers—into paving material for athletic or recreational surfaces. SOEX employs a more ecumenical approach: all types of shoes are welcome.
Shoes are first shredded, then run past powerful magnets to remove ferrous metals. Next, a delamination process eliminates non-ferrous metals and textile fluff. Air separators divide what’s left into rubber, leather and foam. And finally, granulators grind those individual components into feedstock for rubber mats and soles, bonded leather and insulation boards and foam padding, respectively.
“This year, we will scale up the project to a steady production,” said Pailak Mzikian, SOEX head of business development.
There are a couple of downsides to this system, Rahimifard noted. For one thing, the sorted materials are downcycled, which means they’re of diminished quality and therefore less valuable. Neither can he always make a clear business case for the cost of collection and transportation.
“When we talk to some startup businesses in this field, they say recycling can pay for itself if the shoes could be collected and transported for short distances within a heavily populated urban area. But an annual return of 5-10 percent for such businesses is not big enough to make the initial investment,” he said. “When the return becomes somewhere like 20 or 25 percent, that’s when the businesses become interested in this as a viable model.”
Building better components
Certainly brands aren’t inured to the idea of footwear waste. The biggest names in the shoe business are tackling the issue in their own ways.
Nike, for one, approaches waste as an issue it can approach from both ends. There’s the aforementioned Nike Grind program, of course. Then, in 2012, Nike introduced Flyknit, a knitting technology that creates uppers in a single, seamless piece.
The concept was, at the time, groundbreaking. Compared with traditional cut-and-sew footwear, Flyknit shoes leave behind 60 percent less waste, according to Nike. In fact, the sportswear giant claims it has saved nearly 3.5 million pounds of waste—equivalent to the weight of 2.5 million basketballs–since the technology was introduced.
In its 2016 sustainability report, Nike revealed that 71 percent of its shoes and apparel today contains recycled materials, some of it derived from its own production leftovers. All Flyknit shoes today, for example, comprise recycled polyester derived from post-consumer plastic bottles.
“At Nike, we believe waste is an innovation challenge and a source of value,” said Cyrus Wadia, vice president of sustainable business and innovation at Nike. “For more than 20 years, we’ve been looking for ways to reduce our environment footprint and find new ways to turn waste into value streams.”
In his “Letter from the CEO,” Mark Parker noted that materials account for 60 percent of a Nike shoe’s environmental impact. “Low-impact and regenerative materials” such as manufacturing scraps are therefore key to creating closed-loop products with lithe footprints.
“From an impact standpoint, materials matter the most,” Parker said. “One of the keys to our success will be to develop a new palette of sustainable materials. Coupled with smarter designs, we can create products that maximize performance, lighten our environmental impact, and can be disassembled and easily reused.”
Last October, Nike debuted Flyleather, a composite material that it called its “most sustainable leather ever.” Unlike traditional full-grain leather, Flyleather comprises parts of a cow’s hide that’s typically discarded during the leather-making process—up to 30 percent, per the company.
Nike grinds up the scraps, combining them with synthetic-blend fibers and polyester fabric before fusing everything into a single material. After a finishing process that includes embellishments such as pigmentation, the material is placed on a flat roll for cutting, a technique the company says reduces waste even further because there are no awkward curves to navigate.
To further explore the reuse and regeneration of materials, the sportswear company has teamed up with the nonprofit Ellen MacArthur Foundation, a champion of the circular economy.
“We envision a transition from linear to circular business models and a move toward closed-loop products: designed with better materials, made with fewer resources and assembled to allow easy reuse in new products,” Wadia said. “This will involve up-front product design, with materials reclaimed throughout the manufacturing process and at the end of a product’s life.”
Nike isn’t alone in its pursuit of low-impact or regenerative materials. Adidas also has a line of shoes called Primeknit. And, in collaboration with the creative think tank Parley for the Oceans, it’s been cranking out millions of sneakers made from recovered ocean plastic since 2016.
Over the years, Timberland has experimented with fishnets, coffee grounds, even car tires. More than 270 million plastic bottles have since found new life in its footwear, the company said.
And in 2011, Puma unveiled a version of its classic suede sneaker with a 100 percent recycled upper and an outsole derived from rice husks. The year after, it feted InCycle, a line of Cradle to Cradle–certified goods that included a biodegradable sneaker.
Expanding down the supply chain
Still, recycled materials and other material innovation can pose complications further down the stream, Gullingsrud said. Without explicit guidance, collections and sorting facilities seldom know what to make of them.
“Can you imagine a collections and sorting facility, like I:CO, receiving [Puma’s Incycle sneaker]?” Gullingsrud asked. “Are they going to know that it’s biodegradable? The thing that they see is this is a shoe.”
While the shoe “definitely represented a beautiful Cradle to Cradle design execution,” Gullingsrud said, there needs to be “embedded intelligence” in these novel items.
“Just because it’s circular design doesn’t mean it’s going to be circular execution,” she added. “Designers can’t design in a silo. It’s a supply-chain collaboration somehow.”
Designing shoes for ease of deconstruction, a concept that brands like Timberland and Patagonia have flirted with, faces a similar hitch. “You can’t design for disassembly without having some sort of intention and instructions later on,” Gullingsrud said.
Unless brands are willing to take on collections and sorting themselves, there needs to be some level of industry-wide consensus among all the stakeholders in the value chain, Gullingsrud said. And that includes the consumer. “We’re a part of the supply chain now, so we need to make sure that these things go to right place, too,” she said.
For Colleen Vien, sustainability director at Timberland, the biggest challenge to circularity for footwear is changing the way shoes are designed, manufactured, and recovered at the end of their life.
“That’s basically the whole business cycle, and it will take time to shift an entire industry,” she said.
And brands don’t have to have the financial wherewithal of a Nike or an Adidas to nudge the needle.
“Designing footwear with the fewest possible components and simplifying material choices is a good place to start,” she said. “The less that goes into the production, the less waste is created during production and at end of life.”
But perhaps just as salient, shoes should be able to withstand the test of time. “Our commitment to build durable products that last several years is our first approach to combat end of life disposal,” Vien said. “[Shoes should lead] a long life with many great experiences. If only there were a way to have footwear talk—the stories of their journeys of a long life would be quite a biography!”