Ethical and environmental debate is spurring researchers to look for more advanced alternatives to leather.
The fashion industry doesn’t just have a monetary price tag – it also comes with a hefty toll on the environment. Figures from the European Parliament suggest that the textile sector is the third-largest source of water degradation and land use, with textile purchases in the EU generating around 270 kg of CO2 emissions per person. On top of that, estimates suggest that less than 1% of used clothes are recycled into new articles of clothing.
The leather industry has received especially strong backlash in recent decades, largely from animal rights groups but also on account of the sector’s poor environmental credentials. The leather industry’s reliance on animal agriculture contributes to deforestation and greenhouse gas emissions. The strong chemicals required during the tanning of animal leather have also been a point of concern, as these chemicals may be introduced into the environment through waste or accidental releases, resulting in damage to local ecosystems.
In response to these criticisms, the fashion world has begun to turn its back on the traditional leather industry. In 2018, Helsinki Fashion Week announced, via a press release issued by the animal rights non-profit PETA, that they would be prohibiting leather from their shows to take “an active stand against cruelty to animals and the damaging environmental impacts that the use of animal leather brings with it.”
This shift in attitudes, combined with recent advancements in materials science, has given rise to a new industry – that of leather alternatives.
The problem with current vegan leathers
Most non-animal-based leather currently available on the market – often labeled as “vegan” leather – is made from petroleum-derived synthetic polymers, such as polyurethane (PU) or polyvinyl chloride (PVC).
While this synthetic faux leather does largely side-step the ethical and environmental concerns associated with animal products, these vegan leathers are non-biodegradable and are limited to the same constrained end-of-life recycling possibilities as most common plastics. Some studies also suggest that these synthetic leathers may become a source of microplastics as they age.
Bio-based eco-leather
In the continued hunt for a more ecologically sound alternative to animal leather and petroleum-based leathers, scientists have turned to the natural world for inspiration.
Bio-leather alternatives are derived from natural materials, such as fruit peel and pulp, fungal mycelium or bacterial cellulose. By incorporating natural feedstocks, academics and industry R&D partners hope to create even more sustainable, eco-friendly, vegan alternatives with improved biodegradability and longevity.
Mycelium leather
Fungal leather may not sound like a particularly appealing concept, but leathers made from fungal mycelium are gaining traction due to their biodegradability, biocompatibility and low carbon footprint.
Fungal mycelium is the root-like part of a fungus that is responsible for nutrient delivery. It is made up of a network of very thin fungal threads, called hyphae, that give it its distinctive fuzzy appearance.
The concept of using fungal mycelium as a form of textile is not new; indigenous peoples in the United States and Canada have used forest fungi for a wide variety of applications, including as a textile in fabric mats. In Transylvania and surrounding areas in Europe, amadou – a spongey material derived from Fomes fomentarius and similar fungi – is processed by hand and used to make leather-like hats and bags.
On the global commercial stage, mushroom leather is one of the more popular leather alternative options. According to current estimates, fungal-based leather substitutes had a leading 26.6% market share of the bio-based leather market in 2021, with the total bio-based leather market being projected to reach a market value of $97 million by 2027. Major fashion brands, including Adidas, Kering, Lululemon and Stella McCartney have also looked to get in on the mushroom leather action, announcing partnerships and products made with fungi-based leather manufacturers.
Despite the relative popularity of mycelium leather, there are still a number of important challenges facing the sector. Firstly, there is no real consensus over which fungal strain makes for the most optimal final properties and the number of strains tested only reflects a small fraction of the millions of fungal species that exist. Strain selection can also have a significant impact on downstream processing techniques. Additionally, the physical properties of these leathers are not yet on par with traditional animal leather or plastic-based vegan leathers.
Plant-based leather
Plants and fruits are another popular option for generating leather-like materials from non-animal sources. The methods of producing these leather alternatives vary greatly depending on the starting material, but generally, these eco-leathers are made from cellulose that has been extracted from fruit or plant biomass.
Cellulose is a natural complex carbohydrate polymer made up of repeating glucose units. It is the primary structural component of plant cell walls and is also an important dietary source of fiber.
Piñatex®, developed by the plant-based textiles company Ananas Anam, is one of the most well-known plant-based leathers. Piñatex is made from fibers extracted from waste pineapple plant leaves that are generated during the harvest. These pineapple fibers are then washed and purified before being mixed with corn-derived polylactic acid (PLA) to form a non-woven mesh base material. Additional coatings and finishings then turn the material into something similar to leather.
Another popular leather alternative is Desserto® – which has already launched collaborations with fashion and automotive industry giants, including Karl Lagerfeld, Mercedes-Benz and BMW. Desserto is 90% plant-based and is made using fibers and proteins extracted from cactus, which has the benefit of being a hardy plant that can thrive in harsh temperatures and requires much less water to grow than traditional crops.
However, while these products are a popular option for vegans and other consumers seeking non-animal-based leathers, they are not 100% biodegradable as they do contain some amount of petroleum- or plant-based plastics. While some plant-based options are still fully recyclable (as Desserto claims to be), the inclusion of plastics and partial biodegradability may still be a turn-off for some consumers or applications.
Microbial leather
If a plant- or fungi-based leather alternative doesn’t sound like your style, there are other options out there.
Motivated by a desire to produce “post-petroleum” alternative textiles – ones that use no plastics or other petroleum-based compounds in their synthesis – researchers have also begun to experiment with engineered bacteria that can produce the cellulose needed for sustainable leather products.
Nanocellulose is naturally produced by bacteria of the Komagataeibacter genus. Through recent advances in synthetic biology and genetic engineering, scientists have been able to genetically engineer specific Komagataeibacter strains that will produce thicker cellulose films and/or have a higher production efficiency.
In a recent paper published in Nature Biotechnology, researchers from Imperial College London showcased a leather wallet made from bacterial cellulose that not only avoids the use of plastics, but also does not require any harsh chemical treatments to dye the leather a darker color.
This was done by introducing additional genetic modifications to the bacteria that would prompt it to also produce the dark pigment eumelanin, in addition to cellulose films.
“Bacterial cellulose is inherently vegan, and its growth requires a tiny fraction of the carbon emissions, water, land use and time of farming cows for leather,” said lead study author Professor Tom Ellis, of Imperial’s Department of Bioengineering.
“Unlike plastic-based leather alternatives, bacterial cellulose can also be made without petrochemicals, and will biodegrade safely and non-toxically in the environment.”
Microbial leather bags and clothing have been flaunted by fashion brands in recent years, with the material’s flexibility and high tensile strength making it a promising alternative to traditional leather. However, there are several challenges still facing the field, most notably concerning the scalability of production and issues with homogeneity and contamination.
Cultivated leather
One extremely novel approach to sustainable leather-making takes the alternative leather industry almost full circle — back to where it all began, with animals.
Similar to the production of cultivated or “lab-grown” meat from animal cells, these leather-like materials are made by cultivating animal skin cells in a controlled laboratory environment until they begin to form animal hide-like tissues. These tissues can then go through the leather tanning process, effectively producing animal leather but without the need for animal slaughter.
While this kind of cultivation approach is generally positioned as being a cruelty-free way of making leather, rather than an explicitly sustainable one, some lab-grown leather start-ups do suggest that this production method could reduce greenhouse gas emissions and land use due to the lessened need for animal agriculture. However, it is worth noting that the powering of a laboratory environment is also energy-intensive and potentially could limit the scalability of such approaches.
The outlook for alternative leathers
The invention and adoption of such eco-leathers marks an exciting direction for the fashion industry, with high-end and mass-market fashion brands seemingly keen to experiment with sustainable materials to reduce their environmental footprint and offer non-animal-based alternatives for certain consumer markets.
While challenges do remain in terms of scaling up production and improving durability, continued advancement in materials science and synthetic biology could help to propel these materials even further into the mainstream.