It is estimated that 24 billion pairs of shoes are made every year. Many of these will contain materials derived from fossil fuels. That foamy-looking sole on your running shoes? That’s likely ethylene-vinyl acetate (EVA), a type of expanded plastic often made from petrochemicals, and is just one example of the use of synthetic polymers in our footwear.
Consumers are becoming increasingly aware of the sustainability issues surrounding fashion, and the consumption of fossil fuels to feed the latest footwear trends is becoming ever more unpalatable to the eco-savvy consumer.
This is reflected in the growth of the global sustainable footwear market, which is currently estimated at USD 8.5 billion and is projected to grow to USD 13 billion in 2030.
Switching from fossil fuels to sustainable alternatives, whilst maintaining the same performance properties, is not a simple task. However, with increasing demand for eco-friendly footwear, many shoe manufacturers have turned their attention to threading that needle.
The sole is a crucial component of any shoe. It must provide appropriate cushioning and support, but also durability to withstand the 4000 or so steps that the average Brit walks a day.
Synthetic polymers (or more colloquially, plastics) are particularly useful materials to strike the right balance in the demanding performance characteristics required by the sole. Their physical and mechanical properties can be fine-tuned by careful selection of the polymer’s building blocks (monomer units) and the processing conditions. The downside, of course, is that the polymer building blocks are often derived from fossil fuels.
In turn, plant-based polymers are gathering interest. On the macro-level, many of these plant-based polymers are identical in structure to those made by fossil fuels. But the key difference is that – on the molecular level – they are made from building blocks that are derived from renewable plant sources.
For example, one sole-ution offered by Allbirds is their SweetFoam® technology – a bio-based EVA foam sole that is made from renewable sugarcane feedstock that is responsibly sourced from southern Brazil.
Also, running brand Saucony have launched the Triumph RFG (Run for Good), a running shoe that is described as “powered by corn” because it features a corn-based midsole – 55 % of which is made from CovationBio PDO’s Susterra® Propanediol, a speciality diol made from corn sugar. This initiative underscores Saucony’s commitment to include recycled, organic, or renewable materials in everything they make by 2030.
In a similar vein, Crocs, in a collaboration with Dow, are switching out their standard fossil fuel-based Croslite™ material (which is reportedly EVA) with a bio-based version that incorporates Dow’s ECOLIBRIUM™ technology so as to “transform sustainably sourced plant-based waste and by-products into footwear”. This is a key component of their goal to reduce the carbon footprint of their iconic clogs by 50 percent by 2030.
Running company On has gone a step further by making a completely circular road running shoe – the Cloudneo. The shoe is bio-based, being mostly made from polymers derived from castor beans. Moreover, as part of On’s Cyclon™ circularity program, it’s only available via subscription. That is, once your Cloudneo’s are worn out, you give them back to On (getting a new pair in return) and they convert the worn out kicks back into the raw materials to make something new.
Moving upwards from the sole, a whole range of sustainable options are available for shoe uppers, with lots of players operating in this space. An area of particular activity is around sustainable alternatives to leather, as covered by Mewburn attorney Thomas Lonsdale in another recent blog. A good example is bio-based fashion company Pangaia, who have a range of Grape Sneakers that feature “leather” made from repurposed waste from the winemaking industry such as grape skins, stalks and seeds. Not only does this provide a plant-based alternative to animal leather, but it also avoids the troublesome fossil fuels that are typically associated with traditional synthetic leathers made from polymers such as polyvinyl chloride (PVC).
At first glance, the tyre and footwear industries seem like an unlikely partnership. However, look more closely, and the similarities in their products become apparent.
Tyres are typically made from natural rubber that is created from the milky sap (latex) of the “Rubber Tree” (Hevea Brasiliensis) (explored in our earlier blog “Green tyres: wheeling towards sustainable rubber”). The slip resistance and elasticity provided by rubber makes it an ideal material for bearing the load of a vehicle and maintaining traction on the road.
These same properties are also useful for keeping our feet firmly planted on the ground. And so, it’s not surprising that rubber is also a valued footwear material.
Our annual consumption of tyres is huge. It’s estimated that one billion tyres reach the end of their useful lives (as tyres) every year. However, rather than viewing these discarded tyres as landfill fodder, a number of innovators have found ways to “upcycle” tyres into footwear.
For instance, Hankook in collaboration with Tread&Groove have set about producing shoes from Hankook tyres that were doomed for the scrapheap due to minor defects. Here the tyre treads (the patterned tyre portion that contacts the road) of defective tyres are re-purposed as the outsole of a shoe branded as the “HK Groovy”.
Also, Nexen in partnership with French sportswear brand Eider have created a range of trekking boots that feature outsoles manufactured from a rubber by-product created during tyre manufacture.
In the UK, start-up Compound Footwear has found a creative solution to re-purposing end-of-life motorsport tyres. To give an idea of the scale of wastage, over 600,000 waste motorsport tyres are generated in a single season, many of which are destined for the incinerator. To lessen the environmental impact of motorsport waste, Alex Witty – founder of Compound Footwear – has designed a range of footwear with soles created from end-of-life racing tyres. And, at the end of their life, Compound Footwear sneakers can be recycled into 100 % reusable raw materials to make new products.
On the front foot
Eco-consumerism is on the rise. Consumers are becoming increasingly more educated on sustainability, and in turn are demanding more sustainable products and business practices.
In the footwear sector, this demand for sustainability is driving innovation towards bio-based solutions that offer the same aesthetics and performance characteristics as traditional petrochemical-based materials. The examples above represent just a few of the innovations that prove that these demands are not only reasonable, but achievable, and offer a step forward in the journey away from fossil fuel-based footwear.
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