The modern running shoe evolved during the fitness boom of the 1960s and 70s in order to provide comfort and performance benefits for the masses taking to the streets. Shoe designers looked to synthetic materials to enhance the underfoot feel, improve the fit, add durability and reduce weight as well as cost. Today’s ideal running shoe has a resilient spring, efficient energy return, ample cushioning, durable sole, and a breathable, flexible, yet secure upper with a snazzy design. But the materials that give our running shoes those qualities — nylon, polyester, polyurethane, EVA, TPU, synthetic rubber, and textile dyes, to name a few — are part of both an earth-choking plastic problem as well as a devastating carbon emissions crisis.
One 2013 study conducted by researchers at MIT found that a typical pair of running shoes generates a whopping 30 pounds of carbon dioxide emissions, most of which come from the manufacturing process. According to RunRepeat Research Director Danny McLoughlin, if the sneaker industry were a country it would be the 17th largest polluter in the world each year. Additionally, because of the complex ways performance running shoes are constructed, they are nearly impossible to recycle. And we all know how infamously short the lifespan of a pair of running shoes can be if you rack up a lot of mileage. So after serving your feet for a short period of time, they go on to clog up landfills or float down waterways for hundreds of years before decomposing.
Breaking Down a Running Shoe
Let’s start with the upper, which contributes to approximately 42% of a running shoe’s emissions according to McLoughlin’s RunRepeat analysis of MIT’s study. The fabric used to construct an upper is usually nylon, polyester, and polyurethane. Nylon and polyester are types of petrochemicals, synthetic materials that are non-biodegradable. Furthermore, nylon manufacture produces nitrous oxide, a greenhouse gas said to be 310 times more potent than carbon dioxide by some estimates. Not to mention that the splashy colors common on modern running kicks, achieved through textile dyes, involve the use of toxic chemicals which are often discarded by being dumped in water sources and ditches, poisoning local communities. Garment manufacturing is responsible for 20% of all industrial water pollution around the globe and ranks as the world’s second-largest polluter of water.
Moving on, the foamy midsole is responsible for an estimated 30% of a pair of running shoe’s carbon emissions. The most common material used to engineer the midsole is ethylene-vinyl acetate (EVA), defined by its lightweight, responsive underfoot feel, which can be tuned to a variety of densities to provide different rides with varied levels of cushioning, stability and rebound. Runners and designers fell in love with EVA for its performance and durability. But this is a petroleum-based product that can be kept in contact with moist soil for a 12-year period without experiencing any evidence of biodeterioration.
The last few years have also seen the introduction of polyurethane (PU) and thermoplastic polyurethane (TPU), which create the bouncy, durable cushioning of today’s “energy return” midsoles. Though polyurethane scores a bit better than EVA in terms of biodegradability, it’s also made from fossil fuels. Which means that in the production of both EVAs and polyurethane, plentiful amounts of carbon dioxide is spewed into the atmosphere. In the last decade carbon-fiber plates have been added to the midsoles of some running shoes, giving rise to the super shoe revolution. Although it is recyclable, carbon fiber takes a hefty amount of energy to produce. Creating the material is about 14 times as energy-intensive as producing steel, plus it emits a significant amount of greenhouse gasses.
Finally, there’s the rubber outsole of the running shoe that gives it traction, flexibility, and protects your feet and the rest of the shoe from rugged ground. It contributes to 13% of the emissions in a pair of running shoes. These outsoles are typically composed mostly of durable carbon rubber (the same material that tires are made out of) as well as blown rubber — a less durable, lighter rubber often found in the forefoot of the shoe.
Once discarded, these synthetic rubbers contribute to the buildup of tiny plastic polymers polluting oceans, lakes, and waterways. Additionally, the manufacturing process of these synthetic rubbers results in the release of waste that includes several dubious organic compounds, some of which are suspected carcinogens.
While natural rubber is deemed better for the environment, most running shoe companies don’t currently use it. Natural rubber poses its own problems, however. Tropical forests are being wiped out at an alarming rate as they are converted to rubber plantations, threatening biodiversity in the world’s most ecologically rich regions.
Eco Shoes Entering the Market
As the Earth’s progressively warming temperatures and mass species extinction haunts the headlines, the stakes for industries to rapidly evolve have never been higher.
Partially because of the increased media attention given to this environmental crisis, there has been a growing demand for sustainable running shoes. While multiple shoe companies have marketed “eco shoes” over the last few years, not many have yet met the mark for qualifying as a genuinely ecologically sustainable product.
But that might be changing. Recently, three companies have announced the launches of innovative products that may have the potential to blaze a new trail in the construction of truly sustainable running shoes by applying circular economy principles.
On Running’s “Cyclon Movement”
Perhaps the most revolutionary of the three companies is On Running’s recyclable Cyclon shoe. The Swiss shoe company recently announced plans to release the shoes in the fall of 2021. But rather than buying a pair once, the consumer pays $30 per month for a shoe subscription. The idea behind the unique subscription model, says On Co-Founder Casper Coppetti, was to ensure that the shoes would actually be returned to On so they can be recycled.
“One of the problems with recyclable products is that people are not going to give them back,” explains Coppetti. “The thought of actually sending them back to the store is not something that is ingrained in our consumer habits.” The subscription idea came up as a way to resolve the behavioral problem. “Basically the thought was if you don’t own it, you have to give it back.”
The shoe is made out of two similar polyamides: PA11 and PA12. The entire upper of the shoe is made of PA11, which is a bio-based polyamide derived from castor beans — a “zero waste” product that became popular amidst the oil shortage in the 1970s because it was found that biofuel could be made out of the plant.
“That’s how we got the idea,” says Coppetti. “If you can make fuel, you can also make foams.”
The outsole of the shoe is currently made out of PA12, which, unfortunately, is not yet plant-based. However, according to Coppetti, the company is aiming to also be making the outsole out of castor beans by the time the shoe ships next fall.
“The beauty of this is we can take this whole shoe and shred it, melt it, and make a new compound out of it that will again go into a shoe, or a part of a shoe,” says Coppetti. To facilitate efficient recycling, the white shoe contains no textile dyes. After it is washed, ground up, and melted, 100% of the material will be reused, allowing the shoe to be recycled 7 to 8 times on average. Because the bulk of CO2 emissions in a pair of running shoes are in the material processing and manufacturing phases of the product, Cyclon’s high recycling rate will cut these emissions down to 50% of what a regular On running shoe would have. Additionally, the waste generated from the production of the shoe could be slashed by half thanks to the smart design.
On claims that the shoes should last at least 373 miles (600 Km) before you need to turn them in for a new pair. On average, runners go through a pair of running shoes every four to nine months, so On sends subscribers an email around five and a half months after they receive a pair of Cyclons to inform the customer that they are eligible for a new pair. As for higher mileage runners, Coppetti says that if you can prove with Garmin or Strava data that you’ve hit a certain number of miles, On will replace the Cyclons earlier. Whenever you are ready to trade in the shoes, On will send you a box of new shoes that doubles as a return ticket for the old shoes. You simply put the old pair in the box and send them back to On.
“We didn’t want to overly complicate the subscription, we wanted it to be like Netflix or Spotify,” says Coppetti. “It’s 29 bucks a month, and basically you have your running shoes coming whenever you need.”
On’s goal is to make it as straightforward as possible while also fostering more personal consumer-company relationships.
“We want to create a community and we want to engage [with them],” says Copetti. “We also see that people who are actually subscribing, they want to have a conversation because maybe they are ‘woke’ or feel like maybe this is a bigger thing.”
Coppetti points out that the running industry has traditionally been backwards in its approach to sustainability issues. Namely, the idea that sustainability means a compromise in a shoe’s performance. The Cyclon aims to break this old “sustainability vs. performance” duality in thinking, becoming a conceptual blueprint the brand can apply to future products.
“Cyclon is really a whole movement”, says Coppetti. “We’re already working on a shirt that is made of recycled materials. So you can have a shirt that turns into a shoe or a shoe that turns into a shirt. And actually, the material has pretty good performance and metrics.”
The France-based brand Salomon is also introducing a recyclable performance running shoe, the Index.01, which it says is designed to be easily disassembled and recycled at the end of it’s time on your feet without mixing material. It will be available for purchase in spring 2021.
Each person who buys a shoe will need to register on Salomon.com with his or her proof of purchase. When the shoe is worn out, you fill out a request on the website to download a return shipment document, free of charge. You then mail the shoes back in a box with the shipment documentation on it. To push clients toward actually recycling the shoe, Salomon will send customers a reminder every 3-6 months that their shoes are recyclable and should be returned.
The shoe, backed by three years of research, is developed to reduce material waste and lessen the environmental impact of footwear by using circular lifecycle principles.
The Index.01 is made primarily of recyclable polyester and a nitrogen-infused thermoplastic polyurethane (TPU) foam called “INFINIRIDE.” According to Salomon, at the end of the shoe’s life, the recycled polyester upper and thermoplastic polyurethane base unit are deconstructed and recycled separately through regional recycling programs.
“After removing the sock-liner (which will be incinerated), we will clean the shoe and then separate the two material families,” explains Salomon’s footwear sustainability manager Olivier Mouzin. “The Polyester will be sent to our local partner to produce a new yarn, which will be used to produce new clothes or shoes. The Thermoplastic Polyurethane (TPU) will be used to mold new technical pieces like ski boot shells in Europe or shoe chassis in China. To craft such a recycling process and commit to collecting, recycling and keeping the material as pure as possible really is a big step forward in pioneering the future of the circular economy in footwear.”
But, is the manufacturing process less energy consuming than a typical pair of running shoes? Salomon thinks so.
“We reduce the number of parts in the upper of the shoe, we use recycled material for the upper and the sock-liner, and the outsole is made of TPU and not rubber (which is less energy consuming),” says Mouzin. “We currently have measurement analysis ongoing to compare the energy efficiency of this shoe to another shoe in our range with the same level of performance.”
The Index.01 is the product of Salomon’s Play Minded Program, the brand’s sustainability initiative that addresses the company’s impact on the environment. Since 2017, Salomon says that it has taken steps to include circular economy principles into its processes.
“The first step is to create less impactful products through our choice of materials, the product construction, the production process and the supply chain,” Mouzin outlines. “The second step is to create recyclable products and drive the recycling process in order to loop the material usage and keep the material as pure as possible so that it can be used several times in new products.”
A typical problem with recycled products is that material families end up blended together into a kind of “soup” that can’t be used later on. Salomon managed to overcome this for the Index.01, paving the way for future sustainable products and manufacturing methods in the company.
“For sure, more Salomon recyclable products and less impactful products will be coming in the future, as well as more durable products that are made of more sustainable materials,” says Mouzin. “These are exciting times and we are eager to charge forward.”
Reebok’s Forever Floatride Grow
Reebok has also launched its own plant-based performance shoe, the Forever Floatride Grow, with a midsole made of castor beans along with “a breathable eucalyptus tree upper,” and a sockliner constructed of algae foam. The outsole is made from real rubber trees to give it durability. Reebok claims that the shoe boasts a highly cushioned and responsive midsole.
“Forever Floatride Grow is made for runners who care about performance and want to feel good about the products they use daily,” said Emily Mullins, Product Director at Reebok, in a press release. “This shoe is the result of a long journey to create a plant-based running shoe that looks and performs like other best-in-class footwear and can withstand running a marathon.”
One of the challenges with making sustainable performance running footwear out of plant material is that the shoes need to be able to tolerate impact. Unfortunately, petroleum-based plastic holds up very well. With this shoe, Reebok claims it has been able to use plant-based plastics that meet the mark on durability.
“We focused on process innovation such as how we make things, who we partner with and where we make them and ended up with a really innovative and unique product,” said Mike Andrews, Advanced Development Director at Reebok. “We conducted extensive testing to ensure athletes wouldn’t feel any difference when running in a plant-based shoe.”
The company has been making genuine sustainability efforts over the last few years, aiming to create more of its products out of plant-based materials and focus on creating products by recycling materials. Additionally, Reebok claims that it is committed to reducing virgin polyester from its material mix with a goal of total elimination by 2024.
Are “Green” Shoes Enough?
Are technological solutions that are generated through a private company in a free market really capable of addressing large scale ecological challenges? There is a reasonable amount of skepticism concerning whether green consumption is an effective and lasting solution for climate change. Undoubtedly, On, Reebok, and Salomon have taken commendable, innovative steps forward to take on certain aspects of a colossal problem.
Of the three brands, On has set the boldest goals to go above and beyond making sustainable products by pushing forth a paradigm shift in running product economy and becoming a part of large scale systemic solutions to climate change. Recently, the brand joined Science Based Targets — a gold standard in sustainability for organizations — underscoring its commitment to efforts that will help keep global temperature increases limited to the 1.5°C mark above pre-industrial levels set in the Paris Agreement. On aims to do this by decoupling their resource use from their company growth, making changes to company infrastructure to become more energy efficient, and redoing its packaging to reduce the carbon footprint of the company’s product shipment. After the year 2022, On is aiming to use 100% recycled material for its products.
Coppetti admits that he was surprised at how easy it was to take the lead in sustainability amongst running companies.
“A lot of the solutions are out there, and if you want to do it it’s actually quite doable and it’s not that expensive,” he says, emphasizing that this isn’t a matter of competition. “As an industry, this is also not about beating the other brands. This is perhaps our generation’s biggest challenge, to resolve how we’re using the resources on this planet. Let’s resolve this together.”