For consumers who are often forced to choose between goods that potentially harm animals and those that drip with fossil fuels, the latest breed of plant-based leathers seems to provide the perfect no-compromise solution.
But ersatz hides made from cactus fronds, pineapple leaves, grape skins or apple peels may not be as natural, sustainable or chemically benign as their marketing frequently makes them out to be, a group of German researchers says. Nor can they match up to the structural integrity and technical performance of bovine leather, a byproduct of the beef industry that has drawn scrutiny in recent years for its associations with hazardous tanning practices, threats to worker welfare and deforestation in the Amazon.
While not all plant-based leathers are made the same, many of them employ petrochemical-based polymers, solvents, binding agents or plasticizers that belie their plucked-from-nature narrative, according to a recent study by Filk Freiberg Institute, which tested leather mimics such as AppleSkin, Desserto, Kombucha, MuSkin, Piñatex, SnapPap, Teak Leaf and Vegea. Indeed, one typical approach by the makers of biomaterials, the organization said, is to sandwich the organic matter between layers of polyurethane, apply a polymer-based topcoat and then emboss the surface to give it a leather-like appearance.
Plastic brings with it a toxic burden, however.
Filk, which tests and analyzes flexible multilayer polymer materials for standards organizations such as Oeko-Tex, also identified restricted substances in several of the materials. Researchers found butanone oxime and traces of diisobutyl phthalate in AppleSkin, made from apples, and toluene in Vegea, derived from the stalks, skins and pips of grapes. Piñatex, a product of discarded pineapple leaves, showed diisobutyl phthalate. Desserto, which bills itself as a “vegan cactus leather,” contained butanone oxime, toluene, free isocyanate, the pesticide folpet and traces of diisobutyl phthalate as well.
That plant-based alternatives use polyurethane resins has been something of an open secret, said Martin Mulvihill, co-founder and managing partner at Safer Made, which invests in companies and technologies that reduce people’s exposure to toxic chemicals. Polyurethane, which comprises low-molecular-weight molecules known as isocyanates, often uses involves solvents such as toluene and dimethylformamide in its manufacturing. “It is not surprising that some of these will still be contaminated,” he told Sourcing Journal.
But Raquel Prado, head of research and sustainability at Ananas Anam, the London-based manufacturer of Piñatex, said Filk’s results must be approached with “caution,” particularly since it was published in an open-access journal. (Coatings, which covers the science and engineering of coatings and thin and thick films, notes that it is peer-reviewed.)
Furthermore, just because a substance is “detected,” doesn’t mean it originated from the product, since cross-contamination can occur, she said. The study also doesn’t specify the standard deviation for the compound, its concentration and the detection limit, meaning “no conclusion can be drawn on this basis.”
(Filk told Sourcing Journal that its thermal desorption method for the detection of chemical substances didn’t allow chemicals to be quantified, since its main focus was the physical-mechanical properties of the materials.)
“We have the REACH certificate of compliance for Piñatex, issued by an independent laboratory,” Prado said, referring to the European Union chemical regulation system. “This means there are no harmful substances in Piñatex.”
A spokesperson for Adriano Di Marti, the Mexican producer of Desserto, told Sourcing Journal that its material doesn’t contain butanone oxime or diisobutyl phthalate because the substances aren’t used at the production site. There might be traces of diisobutyl phthalate and toluene in “older versions” of Desserto, but since the current form features a water-based adhesive, no such chemicals are being intentionally applied.
“Our cactus plantations are 100 percent organic and certified by the U.S. Department of Agriculture; we don’t use any chemicals on our cactus fields,” the spokesperson added. “As our products are produced under commercial industrial conditions, the presence of trace quantities of impurities cannot be excluded. But every effort is made to ensure that they are at a minimum level.”
Umberto Bacenetti, CEO of Mable, which manufactures AppleSkin for Italian company Frumat, had a similar grouse about the imprecise quantification of detected substances. “All our materials are produced in compliance with REACH regulation,” he said, adding that AppleSkin is a collection of more than 20 different products made with different processes. “On top of that, some articles comply with proprietary Manufacturing Restricted Substance Lists with stricter limitations than regulatory ones.”
“We believe that the Filk report gives incomplete and misleading information in the struggle of underlining the excellent performances of animal leather in comparison to the sustainable materials that are gaining [a] place in the market,” Bacenetti said. “How come there is no analysis on the hazardous chemicals in animal leather? Heavy metals, azo dyes and many others are commonly used in the tanning industry, but there is no mention of [them] in the report.”
The rest of the report, he said, doesn’t provide information on the type of material that has been tested. “We and our competitors in sustainable materials all have a broad range of materials with different performances and chemical compositions,” Bacenetti added.
Vegea did not respond to a request for comment.
H&M, which has incorporated Desserto, Piñatex and Vegea into its products, told Sourcing Journal that products for its brands are produced with “great consideration for customers’ and workers’ health, as well as for the environment” and that all suppliers must commit to comply with its chemical restrictions. “These restrictions are, as a minimum, always based on the highest legal standard in any of our sales countries and they cover all product types sold by any brand in the H&M Group,” a spokesperson for the Swedish retailer said.
All suppliers and partners of Zalando, which carries products by Desserto and Piñatex, are required to implement a “robust chemical management system” to ensure compliance with the retailer’s Restricted Substances List, said Nicole Stutterheim, a spokeswoman for Europe’s largest fashion e-tailer. In addition to routine testing carried out by the supplier, Zalando “reserves the right to independently test random products as part of a risk-based due diligence system.”
“Regarding the use of plant-based material alternatives to leather such as Desserto and Piñatex, we support the shift towards innovative new fibers and materials with lower environmental footprints compared to conventional alternatives,” Stutterheim said. “At the same time, it goes without saying that all products we sell should be safe and within permitted limits for toxic and harmful substances.” Zalando will be following up on the matter internally, she added.
Leather vs. ‘leather’
Cowhide isn’t necessarily better than its plant-based counterpart, said Mulvihill. While the noxious chemistries in cowhide are different, there is some overlap, he added.
“There is a lot of leather that is also coated with polyurethane, which may have the [same] solvent issues,” he said. “You also have the hide preservation process and tanning process which both use a lot of hazardous chemicals, including halogenated antimicrobials and chromium VI. But a lot will depend on the individual supply chains.”
Certainly, it’s difficult to make an apples-to-apples comparison between bovine leather and its plant-based counterpart, said Tara St. James, founder of textile consultancy Re:Source(d). What matters is investigating each material on a case-by-case basis. Just as “vegan” isn’t synonymous with “sustainable,” neither should all animal leather be tarred as bad.
The Leather Working Group and other organizations, for instance, have been working to clean up the leather supply chain. “An example of this is Be Green, an Italian tannery working towards a metal-free tanning process,” she said. Timberland, to name another example, has partnered with Colorado’s The Savory Institute to promote regenerative cattle-ranching practices.
Not all vegan products are plastic-based, either. Uggs recently debuted a sandal embellished with faux fur derived from Tencel-branded lyocell, which comes from trees. Allbirds is investing $2 million to add Natural Fiber Welding’s “plant leather”—described as the only vegan leather replacement on the market that doesn’t contain any petrochemicals—to its materials lineup.
Suzanne Lee, CEO of Biofabricate, a New York-based platform for biomaterial innovators and consumer brands, says the study’s bias toward natural leather needs to be acknowledged, but it’s also no surprise that the leather industry is hitting back at certain biomaterial startups that have “chosen the strategy of demonizing the leather industry in order to make their product sound preferable.”
Though leather is far from dead, leather replacements are on the ascent. Analysts at Grand View Research anticipate the global synthetic leather market size to expand at a compound annual growth rate of 7.8 percent to reach $57 billion by 2028, which could put the squeeze on cowhide producers. Leather harvested from mushroom roots is arguably a sexier narrative than leather grown from cows. Witness the splashy headlines about Adidas and Stella McCartney’s conceptual forays with Bolt Threads’ animal-free Mylo “unleather.” (Mylo wasn’t included in Filk’s study.) In short, if the traditional leather industry has the opportunity to pounce, it’s going to take it.
“[Leather manufacturers] know that some of the chemistries being used in ‘vegan’ leathers [are] the same or worse than what they use in traditional leather,” Lee said. “Some biomaterial producers are at fault for not being transparent, arguably deliberately obfuscatory, by not revealing the exact percentage of bio content and what the remaining percent is.”
Brands must shoulder some of the blame for the incorporation of synthetics in certain plant-based leathers, too. While many materials, such as Piñatex, started out as 100 percent plant-based out of a “genuine desire” to avoid any harsh chemicals or finishes, “it’s actually the brands themselves who are not happy with the level of durability offered by pure plant fiber materials, that in their demand for improved performance, force innovators to compromise by adding a synthetic finish to improve wear and tear,” Lee said.
Still, Lee admits that the fashion industry “seriously needs to level up” its understanding of biomaterials, which “mostly aren’t made up of 100 percent bio content, nor does the term ‘biomaterial’ in any way indicate biodegradability of any kind.”
Standards might provide a useful guide, but navigating the vast landscape of seals and certifications can make for a vertiginous experience, she added. Biomaterials, with their diversity of ingredients and technology processes, can also be difficult to corral under one universal benchmark.
“At the end of the day everyone wants the Holy Grail: a renewable, compostable, high-performing, pleasing material, at the cheap price of petrochemical synthetics,” Lee said. “As far as I know it does not exist. Meanwhile, we live in a world of compromise. As a brand you have to ask: ‘What do we care most about? Is it the origin of a feedstock? Is it the chemistry used? Is it the end of use? Is it the price?”
Filk, which described itself as a “neutral institute,” also expressed a desire for greater transparency on the part of the manufacturers so consumers “have a real choice” about what they’re purchasing.
“So far the materials have no substantial market share compared to leather and synthetic leather; they are rather niche product,” Claudia Franz, a spokeswoman for the organization, said. “This might change [in] the long run.”