The environmental footprint of manufacturing trainers
Leather and synthetics
As described in our guide to ethical shoes, leather produces, on average, over double the greenhouse gas emissions as synthetic leather and also generates chemical pollution during the tanning process.
Cotton and polyester
Trainer uppers are often made of textiles. Cotton is known for its high water, GMO and pesticide usage and it has a moderately high carbon footprint due its heavy reliance upon fertilisers. It is also associated with forced labour in certain parts of the world (see our guide to shoes).
For every kilo of cotton fibre, around 28 kg of CO2e emissions are produced. Some estimates put it at more, and some as less than polyester. Polyester’s other main impact is, of course, plastic waste.
Sustainable alternatives – Producing cotton organically not only eliminates GMOs, but also reduces global warming potential by around 46%. Alternative fibres such as hemp, jute and flax require less water than cotton and have a lower carbon footprint owing to their decreased need for inputs. Many trainer companies are aiming to increase their use of recycled polyester, which comes with a 32% carbon reduction compared to virgin polyester.
Synthetic rubber and foam
These days, most rubber is synthetic and unless marketed as natural, you can assume your rubber soles originated in the petrochemical industry. The rise of sports shoes also made ethylene vinyl acetate (EVA foam), which provides cushioning in trainers, a common ingredient in modern footwear.
Sustainable alternatives – Natural rubber, produced from latex milk that is ‘tapped’ from rubber trees, is not necessarily a sustainable option. The vast majority is produced on plantations in Southeast Asia. Increasing demand for natural rubber, mostly for vehicle tyres, is predicted to drive deforestation in coming years.
Ethletic trainers address this issue by using FSC-certified rubber, and Veja work with traditional rubber tappers to source wild rubber from the Amazon.
A 2013 study from MIT estimated that the total life-cycle emissions of a pair of mostly synthetic trainers was equivalent to 14 kg of carbon dioxide. That’s roughly the same global warming impact as a 50-mile trip in an average petrol car and half a day’s worth of an average UK citizen’s carbon footprint.
What was particularly interesting is how manufacturing made up 68% of synthetic trainers’ carbon emissions. This means that, when extensive animal products like leather aren’t included, it is the complexity of production that contributes the most to trainers’ carbon cost. Hundreds of manufacturing and assembly steps means the energy used in production is very high.
There are substantial differences between models. According to Nike, its best performing trainer had a footprint equivalent to 4.3 kg of carbon dioxide, while the production of its Air Force 1 model emitted 16.8 kg per pair.
For a huge consumer sector like shoes and trainers that uses so many synthetic materials, moving en masse to natural products is incredibly hard to achieve. It would also not really be desirable – mass-produced cotton, natural rubber and leather all come with considerable environmental downsides.
This trade-off can be circumvented by opting for sustainable materials where possible: organic cotton, recycled polyester, hemp and other woody plant fibres, and well-sourced rubber.
However, according to the MIT study, the extraction and processing of materials only makes up one-third of the life-cycle emissions of a pair of synthetic trainers.
So, for further carbon reductions, manufacturing processes must be altered. A major issue is that coal use for electricity generation is common in China, India, Vietnam and Indonesia – countries that, together, produce over 75% of the world’s footwear.
Energy demand in production, and thus carbon emissions, could also be reduced by making designs simpler and manufacturing easier and faster. The company Allbirds produces many of its trainers with a ‘one-piece’” upper, and big brands are beginning to move in this direction too. Nike’s ‘Flyknit’ model follows a similar idea which also cuts waste – the ‘Free Flyknit’ ends up with an impressively low carbon footprint of 5.4 kg per pair.
However, while a number of companies have either adopted, or begun work on, science-based carbon-reduction targets, and might claim notable carbon reductions for certain lines, there are no signs of them cancelling their more damaging products.