Innovative material solutions inside the Sonnenwagen Covestro Æthon

More sustainable PU seat foam from old car seats – comfort meets circularity.

From discarded car seats to a new driver’s seat: the Sonnenwagen Æthon demonstrates circular economy in action with chemically recycled PU foam. The material delivers the same comfort and durability as virgin foam, while reducing waste and fossil dependency. As a proof of concept, it shows the pioneering recycling of Covestro can open the door to circular solutions in future mobility.

Mass balanced Vulkollan® for battery protection under extreme stress

Extreme race conditions demand maximum battery reliability. That’s why the Sonnenwagen Æthon integrates a vibration-damping layer made from recycled Vulkollan® foam. Our new recycling process recovers more than 90% of end-of-life elastomers and cuts the carbon footprint by up to two-thirds compared to virgin Vulkollan®. A pilot plant is already being prepared for scale-up — proof that this innovation not only stabilizes power supply on the track, but also sets new standards for circularity in the elastomers industry.

Thermally conductive polycarbonate for safe and stable battery performance

Managing heat inside the battery is critical for performance and safety. For this, Team Sonnenwagen relies on Makrolon® TC120FR. The flame-retardant polycarbonate is thermally conductive yet electrically insulating, preventing hotspots and help extending battery life. With a thermal conductivity of 0.8 W/mK in-plane and 0.2 W/mK through-plane, it ensures effective thermal management. Injection molding allows for compact, precise geometries, while bonding tests with SikaForce® 821 demonstrated robust composite structures for reliable cell integration. The material is also colorable and designed to meet the highest safety standards.

Impact-resistant polycarbonate for lighting under extreme conditions

Lighting needs protection that is both tough and transparent. For the headlamp covers, extruded sheets of Makrolon® ET3113 RE were thermoformed into shape, delivering high impact strength, excellent light transmission, and a significantly reduced carbon footprint compared to conventional grades. To secure long-term durability, the deep-drawn parts were coated with the Momentive Silfort® PHC 587C2 system, which provides excellent scratch resistance as well as UV and weathering protection. The result: headlamp covers that guarantee clear vision in some hardrace conditions.

Lightweight energy absorption for safety in case of impact

Protecting both driver and battery is critical in solar racing. That’s why the Sonnenwagen Æthon integrates crash absorbers made from Baysafe® EA 64IF81. This PU material combines very high energy absorption at minimal thickness with stable performance across temperatures ranging from −30 °C to +80 °C. Thanks to excellent adhesion properties, it can be joined in-mold or glued to metal and plastic parts. Its low viscosity during processing also enables thin-walled or complex geometries — making it a versatile solution for safety-critical applications.

Efficient heat management with Makrolon® TC629 RE

Heat management in LED systems is a challenge usually solved with metal. In the Sonnenwagen Æthon, this task is taken over by Makrolon® TC629 RE — a thermally conductive polycarbonate that combines high thermal conductivity with low weight and excellent dimensional stability. It allows for slimmer, lighter LED modules while reducing the number of components. Unlike conventional plastics, it withstands thermal stress at high levels and offers broad design freedom, even in combination with other PC materials. As a mass-balanced, bio-circular solution, it also reduces fossil resources and lowers the carbon footprint — proving that performance and sustainability can go hand in hand.

Partially bio-based PU coated textiles for grip, comfort, and more responsibility

Even the driver’s hands touch more sustainability in the Sonnenwagen Æthon: its steering wheel is covered with coated textiles made from partially bio-based INSQIN® polyurethane dispersions. Impranil® CQ DLU and Impranil® DL 1878 are waterborne and contain up to 56 % renewable content. This reduces VOC emissions and the product carbon footprint compared to solvent borne PU systems, while still delivering high performance. Thanks to its high flexibility, the material adapts even to complex steering wheel geometries and provides excellent grip and tactile quality — ensuring both comfort and control.

Lightweight polycarbonate canopy for safety and visibility

Protecting the driver while keeping visibility crystal clear: the canopy of the Sonnenwagen is made with Makrolon® ET3113, sourced via Exolon and manufactured at KRD Group. This material combines excellent impact strength compared to PMMA, ensuring improved fracture behavior and enhanced driver safety.

At the same time, high optical quality guarantees maximum visibility on the race track, while mechanical strength with high tensile and flexural properties secures the overall stability of the canopy structure. A lightweight solution that blends safety, performance, and clarity.

Energy-saving coating with high-solid CQ raw materials

When coating the Sonnenwagen, efficiency and sustainability went hand in hand. Together with Lechler, the team applied CQ binders Desmophen® NH and Desmodur®, which combine an up to 48% share of alternative raw materials with cutting-edge performance.

The secret lies in Pasquick® technology: thanks to its higher chemical reactivity, it enables coatings to dry at room temperature instead of the usual 60°C. In automotive refinish shops, where entire cars are usually heated in large ovens, this means a massive reduction in energy consumption.

For the Sonnenwagen, Pasquick® was used as the final clearcoat layer, but it also plays a role in other layers such as primer surfacers. Beyond the solar race car, this technology is already applied in repair shops today – proving that sustainable innovation can also deliver in everyday mobility.

Breathable TPU cushioning for comfort and circularity

For the Sonnenwagen seat, Desmopan® AIR demonstrates how comfort and sustainability can go hand in hand. Thanks to its innovative structure, using a new extrusion-based process called parallel-layered manufacturing (PLM), the material offers customized cushioning with variable densities, optimized airflow, and excellent seating comfort. At the same time, it minimizes waste during production, can be mechanically recycled, and aligns with circular economy principles. Washable and sterilizable, Desmopan® AIR ensures long-lasting performance even under demanding conditions.