In the sustainable fiber sector, “mass balance” has become something of a truth-in-labeling flashpoint. Critics insist there isn’t a verifiable way to ensure that buyers receive what the labels promise, creating room for inauthentic claims that inflate the environmental virtues of certain products. Supporters claim the system makes it easier and cheaper to scale more planet-friendly materials because it doesn’t require “sustainable” and “non-sustainable” fibers to be physically separated, eliminating the need for dedicated facilities.
For Fashion for Good, the accounting technique is key to accelerating the adoption of biosynthetic PET derived from renewable feedstocks such as plants, agricultural residues and organic waste. The innovation platform said that by allowing renewable and fossil-based feedstocks to mix, while matching the amount of renewable input to an equivalent share of output through audits, mass balance can reduce the risk of producers overselling their credentials. Beyond that, it can also enable the industry to expand biosynthetics without waiting for infrastructure to catch up.
“One of the challenges we identified for biosynthetic drop-in polymers is that the absence of large-scale production capacity is preventing meaningful market penetration,” said Eva Engelen, innovation manager at Fashion for Good. “There is a huge infrastructural and economic gap between these earlier-stage biosynthetic production systems and the mature fossil PET supply chains that have had decades to scale. And this gap is leading to a price premium, which is quite significant today.”
On Thursday, the Amsterdam organization launched its Mass Balance Demonstrator project, a collaborative effort to implement—and indeed scale—a model for biomass-attributed PET in textiles. It’s rallying a range of stakeholders, including Bestseller, Beyond Yoga, On, Paradise Textiles, Environmental Resources Management, Indorama Ventures, ISCC System, UPM Biochemicals and Textile Exchange to signal demand on one end and drive investment on the other.
“We want to show that there are brands that are really interested in this type of material,” Engelen said. “It was also essential to include industry in the consortium because they are the ones producing the material. They are the ones creating the data that can be used for the carbon accounting and such.”
But boosting the uptake of bioinnovations is only part of the plan. Another is helping the fashion industry decarbonize more quickly—something it badly needs. The sector’s emissions grew by 7.5 percent to 944 million metric tons in 2023, according to the Apparel Impact Institute, marking the first year-on-year uptick since the environmental nonprofit started tracking them in 2019. Ultra-fast fashion and a growing reliance on virgin polyester were among the factors behind the increase. The petrochemical-based fiber now comprises 57 percent of total global fiber production, it added.
“As the industry works to transition away from fossil-derived synthetics, biobased feedstocks represent one of several important pathways to deliver this,” said Sophie Ridler, recycled engagement manager at Textile Exchange.
Still, biobased PET accounts for a minuscule share of the market—just 0.01 percent of global polyester production, according to Textile Exchange’s 2025 materials market report. The multi-stakeholder group attributed the low figure to issues around price and availability, as well as lingering questions about the sustainability of current versions, which can carry impacts on land, communities, biodiversity and soil health that haven’t been fully measured.
Biosynthetics also face a tough business case. The treatment of biogenic carbon varies across sustainability frameworks, creating confusion for companies trying to determine the benefits. Different life-cycle assessment methods, greenhouse gas accounting approaches and the Science Based Targets initiative can handle the subject differently, making it trickier for businesses to position biosynthetics as a clear decarbonization pathway.
In other words, while there is general consensus that biosynthetics have significant decarbonization potential, proving it is more complicated. That’s something else the consortium seeks to address.
Mass balance has attracted controversy in other parts of the industry. The Better Cotton Initiative, the world’s largest sustainable cotton scheme, has employed the method since its inception, likening it to renewable energy credits. Brands pay farmers to grow a certain amount of sustainable cotton and then receive an equivalent amount of fiber after ginning and spinning, even if it might be blended with conventional cotton.
In 2024, two of the largest clothing brands, H&M Group and Zara owner Inditex, were drawn into a scandal after the watchdog group Earthsight linked their supply chains to Better Cotton-certified farms in Brazil’s Cerrado region that were accused of illegal deforestation, land grabbing and violence against local communities. Earthsight denounced mass balance as a “completely inadequate” traceability tool. BCI later said a third-party audit found no breach of its standard.
Engelen said the concerns are valid. In Europe and elsewhere, legislation is tightening, and brands are increasingly in the crosshairs over greenwashing. Even so, she said, certification frameworks exist that allow mass balance to be used in a “controlled” way. She pointed to the ISCC certification model, which establishes “clear boundaries” for how mixed inputs enter a production system and how the outputs are allocated in the final product.
“These certification methods have to be used to ensure that the final products are correctly using the mass balance chain-of-custody model,” Engelen said. If 30 percent of the feedstock entering the system is renewable, she added, then only a corresponding share of the output can claim to be renewable. The same idea could be applied to other fibers, such as biobased nylon or textile-to-textile-recycled materials.
The Mass Balance Demonstrator project has several overlapping goals, including producing biomass-attributed PET resin and yarns, developing a cradle-to-grave greenhouse gas emissions model, creating a scaling blueprint and sharing insights with climate initiatives and standards bodies. Engelen has broader ambitions, too.
“I think one of my biggest hopes is that we can create more awareness around the system,” she said. “I think a lot of people in the textile industry know about mass balance from the BCI model, but they don’t understand what it could do specifically for PET, for example.”
Engelen is also counting on the project can create a “structured feedback loop” with standards setters and impact organizations by quantifying the decarbonization potential of these materials. That could help shape how mass balance and biosynthetic materials are treated in the future, she said, making it easier for brands to ramp up their use of biomass-attributed fibers.
“Another desired outcome would, of course, be that brands are going to incorporate more biobased materials into their material mix,” she said. “We’ve seen such a surge in textile-to-textile recycled materials. I think it would be really beautiful if we could see a similarly strong demand for biobased materials.”