Scientists Devise Methods to Enhance Eco-Friendliness of Running Shoes without Compromising Performance
Finding the perfect running sneaker can be quite a task, given everyone's unique requirements. Some prefer a well-cushioned shoe, while others prefer a minimalistic design that allows them to feel the terrain below. Some overpronate, and others supinate, meaning they require support in different areas of the shoe: some will want a neutral shoe, while others will want a stability shoe (with arch support to correct overpronation).
If you're also concerned about the environmental impact of your sneakers, the process can become even more daunting, as greenwashing and not-quite-true claims about a company's eco-friendliness abound.
Luckily, we spoke to materials expert and avid runner Tony Ryan, who sheds some light on this confusing subject.
Tony Ryan OBE is a professor of physical chemistry at the University of Sheffield, UK, and the founding director of the *Grantham Centre for Sustainable Futures*. He focuses on the global challenge of the food, water, and energy nexus and delivered the televised Royal Institution Christmas Lectures in 2002. He was awarded an OBE in 2006 for "Services to Science."
So, what makes a sustainable, eco-friendly shoe?
"What does sustainable mean?" Ryan questioned. "Let's say you want the lowest greenhouse gas emissions per running shoe, then you can test that via a life cycle analysis (LCA) and do a comparative LCA between different materials and different constructions."
A sustainable shoe should be biodegradable at the end of its life. Shoes need to withstand the moist, warm environment of the human foot and the microbes that live there without breaking down, so most shoes are made from fossil-based materials. "The reason that the materials aren't biodegradable is that they need to survive," Ryan explained. "The only exception is if the sole is made from natural rubber - that comes from a resilient tree. However, it's been so chemically treated, with cross-linking to strengthen the polymers, that it's essentially not biodegradable anymore."
Brands claiming biodegradable shoes are likely telling a fib, according to Ryan. They might claim something is made from a natural material such as corn starch, but it's much the same process as making plastic from oil. "Rather than starting from oil, corn starch is made into polylactic acid (PLA)," Ryan said.
This is biodegradable, but often only in an industrial composter, something the average consumer doesn't have access to. "You need to look at the small print," said Ryan.
Why are materials largely non-recyclable in running shoes?
Running shoes are made from a variety of different plastics, most of which cannot be recycled together. The shoes are built with multiple parts, each with different functions, requiring multiple materials to achieve them all.
"There'll be polyethylene, vinyl acetate, or polyurethane," Ryan said. "There might be an airbag, there's usually an insole." All of these materials are synthetic polymers that serve specific purposes in the shoe.
Even leather shoes are not just made from leather; a leather shoe will have various other materials, like stitching and glue.
Ryan explained that to recycle running shoes, you'd have to disassemble the shoe completely, which would be difficult and not practical. The materials cannot even be used to create the same product as their quality is diminished through the recycling process, a process known as "downcycling."
Can sustainable running shoes match non-recyclable materials in terms of durability, safety, and running performance?
"It's a conundrum," said Ryan. "If you want to get something that's the lowest greenhouse gas emissions per running mile while maintaining running performance, it'll be monstrously expensive to produce."
So, the answer is "perhaps - but we're not there yet."
In terms of materials, sustainable shoes often incorporate organic cotton, recycled rubber, recycled plastic, or plant-derived resources like castor bean-based nylon, bio-based foams, and corn or grape fibers[1][2]. They may also be vegan, using no animal-derived products. Brands tend to prioritize low-impact manufacturing, sourcing materials and manufacturing locally to reduce transportation emissions, and seeking third-party certifications for transparency and responsible sourcing practices[3][5].
End-of-life considerations are also key, with companies designing shoes for durability and repairability, offering recycling and take-back programs, and using biodegradable or compostable materials whenever possible[1].
To shop more sustainably, keep an eye out for greenwashing, checking the authenticity of a brand's claims and researching their production processes and materials sourcing practices. Buy second-hand, refurbished, or overstocked products to extend the life of shoes and divert them from landfills. Finally, consider purchasing fewer pairs of shoes and repairing or recycling them when possible.
[1] Sustainability in Shoe Manufacturing: An Overview. (n.d.) Retrieved June 13, 2023, from https://www.researchgate.net/publication/332395398_Sustainability_in_Shoe_Manufacturing_An_Overview[2] Kamandar, S. G., & Haq, R. A. (2019). Sustainable materials and sustainable products design in design and manufacturing industry. IOS Press.[3] The Future of Sustainable Running Shoes. (2021, March 19). Retrieved June 13, 2023, from https://www.runnersworld.com/gear/a32781694/sustainable-running-shoes/[5] Material Matters: Building A Sustainable Future for the Fashion Industry. (2019, November 19). Retrieved June 13, 2023, from https://www.mckinsey.com/industries/retail/our-insights/material-matters-building-a-sustainable-future-for-the-fashion-industry
- Tony Ryan, a professor of physical chemistry and the founding director of the Grantham Centre for Sustainable Futures, emphasizes the importance of a life cycle analysis (LCA) to determine the lowest greenhouse gas emissions per running shoe.
- In Ryan's opinion, a sustainable shoe should be biodegradable at the end of its life, but most shoes are made from fossil-based materials that are refined to withstand the warm, moist environment of the human foot.
- Brands claiming biodegradable shoes may be misleading consumers, as these shoes are often only biodegradable in industrial composters, not in home composters or natural environments.
- Recycling running shoes is challenging due to the variety of different plastics used and the difficulty of disassembling the shoes.
- Sustainable running shoes may incorporate materials like organic cotton, recycled rubber, recycled plastic, or plant-derived resources, but maintaining durability, safety, and running performance while reducing greenhouse gas emissions can be costly.
