Text: Jean François CabreOriginally published, in French, on www.lacaveajaife.fr and reproduced with the express permission of the author.

Today we are going to talk about sustainable development in the world of footwear and more specifically about the carbon footprint. We will try to put here some figures on the carbon impact of a shoe and try to see in which direction the different brands are going. This is the first part of a small series where we will share some figures, areas for improvement and innovations in this field.

It's pretty hard to put precise numbers into a model, even if it seems important to me not to be subjective. So I mostly relied on an article by Lynette Cheah called Manufacturing-Focused Emissions Reductions in Shoe Production and some data I got from other sites. If you think that the fashion industry (in a broad sense) has no impact, I invite you to read this report: 2.1 billion tons of CO2, 4% of global emissions in 2018.

Life cycle analysis

To analyze the impact of a product, there is a tool that allows you to have a global vision of the raw materials in the withdrawal of the product: it is the life cycle assessment (LCA or LCA in English for Life Cycle Assessment). This is all codified in ISO 14040. The review by L. Cheah is based on an ASICS Kayano 17 (yes, it's a bit dated, but it's good for reference).

Each phase has a different impact on the carbon footprint of the final product: 97% of the total is achieved through 2 phases: material extraction and manufacturing with 4 kg (+/- 0.36 kg) and 9 .5 kg (+ / -2.7 kg) for a total of 14.2 kg of CO2 for a pair of shoes.

Few brands publish figures on the carbon footprint of their shoes. Nike did so in 2020 by posting a few sizes including the Vaporfly at 16.6kgCO2 per pair, the Pegasus 10.3 and the Free FlyKnit at a good 5.4kgCO2eq but without showing the details of each contributor. Allbirds, known to be involved in the matter, claims that their running shoe started out at 9 kgCO2eq before turning neutral.

After this overview of the carbon footprint of footwear, let's go into detail. It is necessary to do this analysis to later be able to implement the improvements to reduce the total footprint.

The materials

Going into more detail in the materials part will allow you to understand certain choices made by certain brands in part 2 and 3. The upper part is made of polyester and polyurethane, the midsole is olefinic copolymer and the sole is made of rubber and the Cellulose packaging: this represents 75% by weight of the shoe and 67% in CO2 emissions.

It is interesting to see that the upper part represents 41% of the CO2 impact and PE and PU materials 57%, only 6% for the cellulose of the packaging. It is important to note that one third of emissions go to waste: a significant source of costs and emissions that is invisible to the end user.

If we look at other studies, we find that the emission of PU in 2010 is slightly less than 5kgCO2eq / kg, the EP around 2kgCO2eq / kg the same as EVA (No, they do not pay me a license at €3,800 in ecoinvent by the figures). So we'll get for a pair at 620g rather than something between 3.1kgCO2eq and 1.24kgCO2eq in a finished product vs. 2.6kgCO2eq in Cheah's study. For information, carbon fiber rounds the 15/20 kgCO2eq/kg, we can understand some of the value differences on the VaporFly. We can estimate around 1 kgCO2eq for the plate.

The manufacturing

Manufacturing involves many stages of cutting, gluing, assembly, compression, injection, by different processes and therefore this necessarily consumes electrical energy, but also carbon for the sole to be able to heat it (according to Cheah's study).

Most of the factories are located in China or Southeast Asia (Taiwan, Vietnam…). China mainly produces its electricity through coal like Taiwan where in Vietnam this is only 40%, which produces a large amount of CO2 and therefore has a direct impact on the carbon footprint of the shoe.

Electricity accounts for 4.4 kgCO2 eq per pair of shoes (in Cheah's study an assumption of 0.88 kgCO2eq/kW was made) and the use of coal to heat the equipment needed to make the soles shows 5 kgCO2 eq. I didn't mention a part here that is the "future" of waste. In Cheah's article, a small percentage is incinerated, so there are no additional emissions. They are deposited in landfills. (Is it better for the planet if you don't value in carbon?). For information purposes, the data used for the calculation dates from a compilation made by Asics in August 2010 and January 2011 to its manufacturers.

If we delve into Asics' sustainability reports we can also read that in 2019, CO2 emissions per pair of shoes manufactured by its Tier 1 footwear suppliers had been extremely reduced, particularly thanks to the drastic drop in the use of coal. The manufacturing carbon footprint went from 2.45 to 1.77 kgCO2eq per pair. These figures seem extremely low compared to the 9kg CO2eq shown above, Tier 1 suppliers may not include 100% of the emissions from a shoe, but we can also point out that Asics does not only produce in China (and in particularly in Vietnam), the 2011 figures are certainly pessimistic and a phase out (or better use) of coal will have a strong impact on value.

Transportation

Your shoe, even before it was produced, already existed! From the raw materials factory to the manufacturers, from the final manufacturer to the countries of distribution, from the distributors to your home but also including the transport of waste: this represents on average 0.3 kgCO2eq per pair according to Cheah's paper. It depends, of course, on the distance between the country of manufacture and your country: count, for example, 0.76 kgCO2eq more for Quebec.

It is low in fact, it represents 2% of the total carbon footprint of the shoe but with a lot of variability because in addition to the country, the last kilometers to get to you can vary a lot.

A strong assumption is the non-use of air transport in the transport of shoes. If we look at the Nike report for 2021, we can see that the brand uses this means to transport its products. It announces a 42 ratio between air and sea, ADEME's figures are closer to double between the 2 means of transport (if we take drag into account). Transportation no longer becomes so insignificant with the plane!

The assumption taken is 0.21kgCO2eq per tonne per kilometer for a truck and 0.011kgCO2eq per tonne per kilometer for containerships, the latest ADEME data shows instead 0.08kgCO2eq per tonne per kilometer for the truck. And 0.006kgCO2eq/ton/km for ships from Asia. These latest estimates lead to a reduction of around 40% of the emissions emitted by transport.

Use

We can already imagine here that the phase of use will be close to 0. The shoe does not emit CO2 due to its use. Only one point is mentioned in Cheah's article. Hand washing will generate a treatment of the water used: 90 liters during the entire useful life of the shoe, that is, 0.03 kgCO2eq.

It depends a lot on the habits of each individual. We will talk again in part 2 or 3, but maintenance is a point that should not be neglected for its durability.

End of life

Emissions associated with end-of-life treatment of running shoes are also low. This is what the study reveals. It will also depend on the practices of individuals and countries. In the United States, 80% ends up in a landfill and the rest is incinerated. These 2 options are not optimal: bury the plastic that we will find everywhere or transform it into CO2.

End-of-life emissions are estimated at 0.37 kg of CO2 equivalent, or just 3% of the total life-cycle impact.

Conclusions

Using the life cycle analysis approach, Cheah estimated that the carbon footprint of a typical pair of synthetic running shoes is 14.2 ± 2.7 kg of CO2 equivalent in 2011. In 2020, Nike published in its annual report a range of 5.4 and 16.6 kgCO2eq depending on the model.

Doing the update exercise of Cheah's estimation, based on the different data from ADEME or Asics, and the reduction in shoe weight (50 grams per pair), we obtain between 12kgCO2eq and 5.1kgCO2eq. Most of the differences come from production-related values: 1.77 kgCO2eq in the Asics report or -27% (Asics data) according to the Cheah report. By contrast, the values ​​available on the ADEME website show an “average” running shoe at 20 kgCO2eq, with a significant part being transported!

And what is 10kgCO2eq? It's 100 km with your car (well, 50 km if you have a Porsche), 5 kg of dough, 2 liters of beers. It is important to implement actions to reduce the footprint of a pair of shoes in a sustainable way. Furthermore, the carbon footprint is only part of the impact of shoe manufacturing: water, eutrophication, acidification of the atmosphere…

Jean François Cabre is passionate about endurance sports and travel, combining his passions for nature and photography. He started racing in 2005 on the roads of western Belgium. He completed his first marathon in 2009 in Millau and his first ultratrail in Bouillon in 2012. I still continue to navigate the road, the path and the mountains to discover new regions.

You can follow him at:www.lacaveajaife.frTwitter: @lacaveajaifeInstagram: lacaveajaife