Foam Filling Stops Heat Spread to Prevent EV Battery Fires
Source： eepower.
Covestro’s flame-resistant foam helps prevent thermal spread in electric vehicle batteries, offering a safe and efficient solution for high-voltage cell designs.
Electric vehicles’ most critical weakness remains tucked inside the battery pack. When just one battery cell overheats and experiences thermal runaway, it can trigger thermal propagation, a domino effect that spreads heat and pressure through neighboring cells. This design flaw has raised safety concerns for years. When China’s GB 38031-2025 safety regulation goes into effect in 2026, battery manufacturers will face strict mandates to contain those failures at the cell level.
Covestro’s answer? A flame-retardant polyurethane foam designed to stop the spread before it starts. Known as Baysafe BEF, this encapsulation material targets the exact point of vulnerability inside modern lithium-ion battery packs: the tight space between cylindrical cells. But what sets it apart isn’t just its thermal performance; it’s how the foam strengthens the battery structurally and fits into the fast-paced workflows that EV manufacturers depend on.
The foam-filled battery demonstrator. Image courtesy of Covestro
How Baysafe BEF Stops the Risk
Baysafe BEF acts as a thermal shield. The foam is injected between battery cells during assembly. It expands to fill every gap, creating a flame-resistant layer. This barrier helps isolate cells thermally, slowing or even halting the spread of heat during thermal runaway. The foam’s chemical structure minimizes thermal conductivity. The material cures cleanly and avoids air bubbles that weaken production. It resists flames and helps contain them.
In early trials, the foam was effective in limiting ignition during simulated failure scenarios, aligning with the goals of China’s updated national battery safety code. That performance is critical as cell-to-pack designs become more popular. When more cells are packed closer together to save space and weight, thermal containment becomes exponentially more important.
However, the foam’s role goes beyond heat. Once the foam is cured, it physically bonds with surrounding components, increasing the battery pack’s torsional stiffness. That added rigidity supports better force transmission, meaning the pack can handle vibration, compression, and crash loads more effectively. In applications like EVs, e-bikes, and portable power banks, that added resilience could translate directly into longer system lifespans and fewer failure points over time.
Manufacturing Compatibility Without the Compromise
Engineers often hesitate to add new materials to production lines, but Covestro built Baysafe BEF with manufacturing in mind. The foam’s viscosity allows it to flow smoothly into narrow voids between cells, even in dense geometries.
Its cure time has been tuned to align with existing polyurethane processing cycles, allowing quick encapsulation without disrupting throughput. It requires no new machinery, excessive dwell times, or bottlenecks in the production line. Battery assembly facilities can apply the foam using standard equipment already onsite, making it a drop-in solution for manufacturers under pressure to upgrade safety without halting production.
This scalability also extends to the foam’s interactions with adjacent materials. Covestro has developed complementary components, like Baysafe EA for crash absorption and a range of shock-dampening covers that work alongside BEF to build a full safety envelope around the battery system.
Thermal runaway and propagation are among electric mobility's most dangerous technical risks. Covestro’s Baysafe BEF tackles it from multiple angles, making it a practical solution for modern battery systems under new regulatory scrutiny.