Balena: Crafting Stella McCartney's Circular Supply Chain

Every year, more than 22.4 billion pairs of shoes are sold worldwide. Most of them contain synthetic materials derived from fossil fuels, especially in rubber soles. This contributes heavily to CO2 emissions, environmental toxicity and industrial waste.

Stella McCartney's new collaboration with Balena aims to offer a practical alternative to this system—starting at the sole.

The two brands have introduced BioCir Flex, a compostable and recyclable material that behaves like plastic when in use but can break down into natural biomass when disposed of correctly.

It is designed to address both Scope 3 emissions and circularity, which involves designing products with their end-of-life use in mind. In the process, they are rethinking the role of supply chains in sustainable fashion.

A material built for the end of the line

Shoe soles are a major contributor to long-term environmental pollution. The National Institute for Health reports that many are made using chemicals like zinc, which add toxic elements to soil and water systems. Traditional soles rely on Thermoplastic Polyurethane—a low-cost, durable plastic derived from petroleum.

Balena’s Head of Product Yael Joyc Vantu says the challenge was finding a material that met performance needs while still being fully compostable.

“That balance of true compostability without sacrificing performance simply hadn’t been cracked yet,” she explains.

“Most biodegradable materials on the market just aren’t built to handle the stress, abrasion, and longevity needed in a sneaker sole. That’s where our material came in.”

BioCir Flex is made from renewable inputs like castor bean oil and polysaccharides—plant-based sugars that are not part of the mainstream food supply. The result is a material that ticks the boxes for durability and low environmental impact. It is even coloured using cinnamon, a natural dye derived from spice waste.

“The real hurdle was how to match the durability and flexibility of traditional fossil-based plastics, using a bio-based material that could also break down at end of life,” says Yael.

“Essentially, we created a material that behaves like plastic when you need it, and like nature when you’re done with it.”

Making circular systems viable

Beyond the material itself, the project focuses on closing the loop through logistics and disposal.

Stella McCartney is introducing a system that allows worn shoes to be returned for recycling. This cuts back on emissions from new sole manufacturing, directly addressing scope 3 emissions—the kind that occur across the product lifecycle, outside the direct operations of a company.

By partnering with industrial composting facilities, Balena ensures that the shoes can break down safely without harming compost quality, land or marine environments. These decentralised compost systems will be essential in creating a circular system that scales beyond small, limited-run projects.

“Now it’s about building out robust supply chains and end-of-life systems and having brands prioritise circularity not just for capsule collections, but across their main lines,” says Yael. “Regulatory momentum and growing consumer expectations are definitely accelerating that shift.”

Price, however, remains a challenge. Thermoplastic Polyurethane remains cheaper, so wider adoption depends on how much brands are willing to invest in their environmental goals. For Stella McCartney, this is already a clear priority.

Supply chains, not slogans

Founded in 2020, Balena exists to solve exactly this problem—developing materials that match the technical requirements of existing plastics while remaining biodegradable and low-impact. Their focus is not just on product development but also on enabling a circular supply chain that loops materials back into the earth, safely and effectively.

For Stella McCartney’s team, the collaboration is the result of years of development and trust.

Ines Ribeiro, Head of Product Innovation and Responsible Materials, says: “Thank you so much to the Balena team, to David Roubach and Yael Joyce Vantu for your trust, tireless dedication, continuous effort and unshakable determination.”

The soles mark a shift in how fashion companies think about material life cycles—from raw ingredient to waste.

With fossil-based synthetics still dominating, Balena’s approach challenges not just the product itself, but the systems that produce and dispose of it.