Fashion for Good Launches Nine-Partner Project to Scale Bio-Based Polyester Supply Chains

Think of it like renewable energy credits: your house draws from the same grid as everyone else's, but the system logs that a wind farm generated the equivalent of what you consumed. Mass balance attribution for polyester works the same way. A plant mixing fossil and biomass-derived feedstocks doesn't physically sort the molecules; instead, it tracks the proportion of renewable input entering the system and assigns that credit to specific products. The garment itself may contain zero plant-derived plastic. The certification, however, says otherwise, and that gap is precisely what Fashion for Good's Mass Balance Demonstrator was designed to stress-test.

The Amsterdam-based organization brought together nine partners on March 27 to pilot the model at commercial scale: brands Bestseller, Beyond Yoga (part of Levi Strauss & Co.) and On; converter Paradise Textiles; polymer producer Indorama Ventures; feedstock supplier UPM Biochemicals; certification body ISCC System; impact consultancy Environmental Resources Management; and standards organization Textile Exchange. The coalition spans the full supply chain, rallying stakeholders to signal demand on one end and drive investment on the other.

"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," said Eva Engelen, innovation manager at Fashion for Good. "And this gap is leading to a price premium, which is quite significant today." Mass balance is the workaround: by allowing renewable and fossil feedstocks to blend at the reactor level, it removes the cost of physically segregating bio-PET at every stage of manufacturing while still crediting the renewable input into the system.

The guardrails are strict by design. Producers cannot allocate more renewable attribution than the actual amount of biomass feedstock entering the system, and once those certified attributes are claimed, they cannot be counted again elsewhere, closing the door on double-counting. Those chain-of-custody controls are what the demonstrator will put through their paces, alongside lifecycle assessments to quantify real greenhouse-gas savings.

What this means for brands is both an opportunity and a communication tightrope. A label that says "made with bio-attributed polyester" is technically accurate under a certified mass balance scheme; one that says "made from plant-based plastic" is not, unless physical traceability to a biomass source can be proven at the product level. Anders Schorling Overgård, material research lead at Bestseller, framed his company's participation plainly: "By taking part in this project we as a company are building experience within mass balance attribution and bio-attributed polyester." The demonstrator is intended to produce not just material but language, giving brands a defensible, regulator-ready vocabulary before green claims legislation tightens the rules further.

The practical decoder for reading any "biobased PET" tag comes down to three tests. Credible messaging names the specific certification scheme (ISCC, REDcert or equivalent), specifies that the claim is mass balance attributed rather than physically traceable, and is backed by a third-party audit covering the full value chain from feedstock to fabric. Fuzzy messaging leans on words like "plant-based," "renewable," or "natural" without naming a standard or clarifying how attribution was managed. If a brand cannot tell you which certification body verified its bio-PET claim, the label is more marketing than accounting.

The urgency behind all of this returns to one number: as of 2023, polyester accounted for 57 percent of total global fiber production. That fossil-feedstock dependency is the lock-in the industry is racing to break, and mass balance, for all its abstraction, may be the most viable near-term lever to do it.