Footwear materials: leather vs synthetics

The skins of other animals have been used by humans for millennia. However, the way that mainstream leather is processed, and the industrialisation of animal farming may be some of the reasons that people are looking for leather alternatives. 

Animal welfare issues with leather

Most companies use the narrative that leather is a by-product of the meat industry. However, leather is economically valuable with high demand for leather-based goods, including shoes. This makes it a profitable industry in its own right, worth over £200bn in 2022. It sustains and feeds the meat industry as a co-product of animal slaughter, and at the slaughterhouse level it’s very difficult to say what ‘comes first’ when different animal bodily parts are shipped off for different industries.

We couldn't find any animal welfare policies for companies’ leather supply chains in the shoes or trainers guides.

Companies were only treating it as a ‘leftover’, thereby ignoring the type of farming or animal welfare issues that their purchases were sustaining. The Leather Working Group certification, which a number of companies use, does not formally include animal welfare and focuses on the environmental impacts of production.
 

When comparing emissions of animal leather with synthetic leather made from polyurethane (PU), even without including emissions from farming, animal leather emissions are still higher:

• animal leather emissions =  17kg CO2e per square metre 
• PU emissions = 15.8kg CO2e per square metre

And, if farming impacts are included, cow leather comes out at 110kg CO2e per square metre.

Using this data and shoe data, Collective Fashion Justice estimates the following:

• pair of shoes made from cow leather carbon impact of 40.7kg CO2e 
• pair of shoes made from PU synthetic leather of 5.8kg CO2e 

Pollution from leather production

To turn it into a wearable product and to prevent decomposition, animal skin undergoes tanning. The majority of leather is tanned using chromium, which is highly toxic to both people and the environment.

Other hazardous substances used in leather processing have been classified by the European Chemical Agency (ECHA) as Substances of Very High Concern (SVHC). Tannery waste is highly toxic and polluting to the environment, plant and animal life, as well as being hazardous for tannery workers.

There are some processes which reduce some of these impacts. 

Chrome-free leather is processed without the use of chromium, heavy metals, and particular acids. It also means that water use is reduced and water is recyclable after use, which is not possible with chrome leather. 

Vegetable-tanned leather uses tannins from trees or other organic fibres during processing.

Buying secondhand footwear gets around some of these issues.

Research has also found that the physical and chemical structure of some vegan bio-based materials including grape leather and apple leather are very similar to purely synthetic leather. Beyond grapes and apples, vegan bio-based leathers for shoes can be made from mangoes, cacti, pineapples, and even fungi. Other novel combinations include corn-based and sugarcane derived materials.

Of course, canvas shoes have been around for hundreds of years and still feature in the ranges of many of the larger companies in our guides. Although canvas can sometimes be synthetic, it can also be made from cotton, flax, or hemp which are all vegan, bio-based, and degradable materials. It's important to note however, that almost all of the bio-based materials currently used in footwear contain some proportion of synthetic material too.

We only found one company, Will's Vegan Shoes, that had a fully biodegradable sneaker, which had textile uppers and was not leather-like. Only Allbirds and Camper had leather-like sneakers and boots with no synthetics in the main material of the uppers. They used a material called Mirum which is 100% bio-based, even though it is too hard-wearing to be officially classed as biodegradable, but both companies also used recycled polyester in their linings.

We recommend looking for vegan bio-based shoes if buying new. They are an alternative to the issues of leather outlined above, and are also moving away from fossil-fuel based synthetics.

What about waterproof footwear?

Generally speaking, well maintained leather, as well as PU and PVC, are used in footwear because of their ability to keep feet dry. So far as we can tell, many vegan bio-based shoe materials also aim to be water resistant at the very least, for example SAYE uses water-repellent organic cotton. 

One problem with waterproofing is that, in 'high-performance' footwear particularly, it can lead to the use of the 'forever chemicals', PFAS. It's worth trying to avoid these in footwear. More information on some of the companies trying to do this appear in our forthcoming PFAS feature.  

Our footwear materials rating

New in 2024 for our guides to shoes and trainers, our footwear materials rating column awarded points to companies that were taking action to reduce the impacts of materials including leather, PVC and PU; designing footwear for recycling or repair; using biodegradable uppers; bio-based uppers; all organic or recycled cotton, or recycled materials; and if the company’s whole focus was on providing lower impact environmental alternatives. 

This way, we capture a holistic view of the impacts that a company’s footwear materials have, rather than only looking at one issue such as vegan or not, or synthetic or not.