Dr. Erin Klokkers is a sustainable materials expert at Continental’s Tires group sector. Together with her team, she is working to steadily increase the use of recycled and renewable materials in tire production. In this interview, she explains how the mass balance approach works and which testing methods ensure that new materials deliver the same safety and performance as conventional ones.
A Continental car tire can contain up to 100 different raw materials. For some of these, we have already introduced recycled or renewable alternatives. Our goal 2030 by latest is to increase the share of recycled and renewable production materials to at least 40 percent. In 2024, the average share was 26 percent, and by 2025 it had already risen to an average of 28 percent.
One specific example is silica derived from rice husk ash – an agricultural byproduct originating, for instance, from risotto rice production. Silica is a filler that helps ensure optimal grip and reduced rolling resistance. We also use polyester yarn made from recycled PET bottles. Depending on the tire size, between nine and 15 bottles can be reused in a single tire. The PET bottles are sourced exclusively from regions where no closed-loop recycling systems exist.
In addition, we use plant-based oils such as rapeseed oil, as well as resins derived from byproducts of the paper and wood industries. We also incorporate recovered carbon black from the pyrolysis of end-of-life tires and recycled rubber from the mechanical processing of end-of-life tires into our production processes.
It may sound complicated at first, but the concept is actually quite straightforward. The mass-balance approach involves replacing fossil-based raw materials with renewable and recycled ones at the beginning of the value chain and then processing them together in existing production processes. The quantities of respective materials are transparently documented and reported. The quantities of respective materials are transparently documented and reported.
This internationally recognized method allows us to gradually increase the share of recycled and renewable raw materials without having to set up separate production lines for each material stream. The goal is to source all materials according to responsible and certified standards. To achieve this, we use certifications such as ISCC PLUS, which verify the sustainable origin and traceability of raw materials. Independent auditors regularly monitor compliance with these standards along the entire supply chain.
All materials, whether conventional, recycled or renewable, must go through the same rigorous testing and approval process. In the laboratory, we test dozens of properties, including elasticity and temperature behavior. These tests are followed by virtual simulations and real-world road testing. A material is approved for production only if it meets the defined safety, performance and efficiency specifications.
In the case of silica from rice husk ash, for example, the source has changed, but the manufacturing process and the resulting material specifications remain the same. This means its performance is identical to that of conventional silica. Every detail matters when it comes to safety and driving performance, which is why the testing requirements for conventional and resource-saving materials are the same.
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