Aspen Aerogels' PyroThin technology represents the most significant advancement in EV battery safety in recent years, using a material that is 97% air to stop lithium-ion battery fires before they cascade out of control. The ultrathin aerogel barrier, now deployed in General Motors' Ultium platform and vehicles from Toyota, Audi, and Porsche, can completely prevent cell-to-cell thermal propagation—the chain reaction that turns a single failing battery cell into a catastrophic pack-wide fire.

The stakes are substantial. The Chevrolet Bolt recall cost GM $2 billion after manufacturing defects triggered thermal runaway in just 16 vehicles. Hyundai spent $900 million replacing Kona Electric batteries. PyroThin's ability to maintain adjacent cells below critical temperature thresholds—even when neighboring cells reach 1,000°C—addresses the fundamental physics problem that has plagued every major EV battery fire.

Understanding thermal runaway in lithium-ion batteries

Thermal runaway occurs when a lithium-ion battery cell enters an uncontrollable self-heating state where heat generation outpaces the battery's ability to dissipate it. The process unfolds as a cascade of exothermic chemical reactions, each triggering the next in a self-amplifying feedback loop that can push temperatures from normal operating range to over 850°C in minutes.

The chain reaction begins at surprisingly low temperatures. Around 90°C, the solid electrolyte interphase (SEI) layer—a protective film on the anode surface—starts decomposing. This exposes the reactive lithiated graphite anode to the organic solvent electrolyte, releasing flammable gases including methane, ethane, and hydrogen. By 130-150°C, the polymer separator between electrodes softens and melts. Once it fails, the electrodes touch directly, creating an internal short circuit with massive current flow.

The separator failure marks the point of no return. Above 150°C, cathode materials begin releasing oxygen, which reacts violently with the already-compromised electrolyte. Self-heating rates exceed 10°C per minute. Peak temperatures can reach 1,800°C in extreme cases—hot enough to melt aluminum.

Cell-to-cell propagation is what transforms a single-cell failure into a vehicle fire. In tightly packed battery configurations, research shows that as little as 12% of the energy released from one failing cell can trigger thermal runaway in adjacent cells. Pouch and prismatic cells share heat with two neighbors; cylindrical cells with six. Hot gases and particulates ejected during venting can reach 1,000°C, directly impacting surrounding cells through conductive, convective, and radiative heat transfer.

Current safety standards require that passengers have at least five minutes to evacuate after thermal runaway begins. China's updated GB38031 regulation, taking effect July 2026, will mandate no fire or explosion for two full hours after a thermal event—a dramatically more stringent requirement that makes advanced thermal barriers essential.

How PyroThin's aerogel structure defeats heat transfer

PyroThin exploits the unique physics of silica aerogel—a material sometimes called "frozen smoke" for its ghostly appearance and extraordinary properties. The aerogel consists of a three-dimensional network of intertwined silica-polymer chains that comprise only 3% of the material's volume. The remaining 97% is air, trapped in nanopores averaging just 5-70 nanometers in diameter—roughly 10,000 times smaller than pores in conventional insulation materials.

This nanoporous architecture creates thermal conductivity lower than still air itself. At room temperature, PyroThin exhibits thermal conductivity of just 24-26 mW/m·K, compared to 26 mW/m·K for motionless air and 40 mW/m·K for fiberglass insulation. The physics are elegant: pores so small that air molecules cannot circulate freely, eliminating convective heat transfer. The tortuous silica framework, comprising such a tiny fraction of total volume, conducts almost no heat through solid pathways. Gas-phase conduction is suppressed because the mean free path of molecules exceeds the pore dimensions.

PyroThin maintains effective thermal resistance even at extreme temperatures—30 mW/m·K at 300°C and 54 mW/m·K at 600°C. The material has withstood 1,000°C propane torch exposure while maintaining structural integrity, and customers have successfully deployed it with lithium-metal batteries that burn at 1,200-1,400°C.

Crucially, PyroThin's thermal performance actually improves under compression. Unlike conventional insulation materials that degrade when squeezed, compressing PyroThin forces out air—which has higher thermal conductivity than the aerogel matrix itself—resulting in enhanced insulation. This property proves essential for battery applications, where cells swell progressively throughout their lifespan and barriers must accommodate significant strain while maintaining protection.

Aspen's manufacturing process creates a dual-function barrier

Manufacturing PyroThin requires the same sophisticated process used for all high-performance aerogels: sol-gel synthesis followed by supercritical drying. Silicon alkoxide precursors are hydrolyzed in ethanol solution, then polymerized into a three-dimensional gel network. The wet gel contains liquid in its nanopores—liquid that must be removed without collapsing the delicate structure.

Standard evaporative drying would destroy the aerogel through capillary forces as liquid-gas interfaces move through the tiny pores. Instead, Aspen uses supercritical CO₂ extraction: the pore liquid is replaced with liquid carbon dioxide, then temperature and pressure are raised above CO₂'s critical point (31.1°C, 73.9 bar). In this supercritical state, there is no liquid-gas interface and thus no capillary stress. The CO₂ simply diffuses away, leaving the nanopore structure intact.

For PyroThin, Aspen integrates the aerogel into a glass fiber reinforcement matrix, creating flexible blankets rather than brittle monoliths. The company applies hydrophobic surface treatments to prevent water absorption and tunes the aerogel chemistry for specific mechanical properties. Standard products come in 2mm and 3mm thicknesses, though custom formulations span 1-4mm for different applications.

The resulting material serves two functions simultaneously: thermal barrier and compression pad. PyroThin's silica-polymer chains act as what Aspen describes as "billions of elastic nano-springs," absorbing mechanical energy while providing thermal isolation. This dual functionality eliminates the need for separate compression pads and fire barriers in battery pack designs—a significant advantage for space-constrained EV applications. The ATB1000 grade provides maximum thermal resistance; the ATB2000 variant optimizes compression performance with slightly lower density (0.16 g/cc versus 0.20 g/cc).

GM Ultium integration demonstrates real-world effectiveness

General Motors' Ultium platform represents PyroThin's flagship integration and provides the clearest window into how the technology functions in production vehicles. The partnership began in 2021—notably, the same year GM faced $2 billion in Bolt recall costs from battery fires—and has expanded to encompass the GMC Hummer EV, Cadillac Lyriq, Chevrolet Equinox EV, Blazer EV, and Sierra EV, plus the Honda Prologue and Acura ZDX built on Ultium underpinnings.

In the Ultium architecture, PyroThin barriers are positioned between individual pouch cells at the cell-to-cell level. The 24-cell modules use an 8S 3P configuration, meaning eight cells in series with three parallel groups. Each large-format pouch cell measures approximately 23 inches by 4 inches, weighing about three pounds and storing 0.37 kWh. Between every cell sits a PyroThin barrier providing passive thermal protection.

Aspen's testing demonstrates the effectiveness. Using 62 Ah CATL prismatic cells with a 2.35mm PyroThin barrier compressed to 50% strain—simulating end-of-life conditions when cells have swelled significantly—engineers triggered thermal runaway in one cell using a 160W heating pad. The adjacent cell reached a peak temperature of just 130°C at the five-minute mark—safely below the thermal runaway threshold. The cell never entered runaway. Monitoring continued for 30 minutes with successful propagation prevention.

The testing revealed another beneficial property: when the trigger cell vents, pressure drops, allowing the compressed PyroThin to slightly expand and actually improve thermal isolation during the critical minutes following initial failure.

PyroThin complements rather than replaces GM's active thermal management system. Ultium packs incorporate liquid cooling loops, resistive heaters for cold-weather operation, and a wireless battery management system (wBMS) that monitors cell health and temperature. The aerogel barriers provide passive protection—a fail-safe that requires no power, no sensors, and no software to function during a thermal event.

Broader automotive adoption spans three continents

Beyond GM, PyroThin has secured multi-year production contracts with major automakers across North America, Europe, and Asia. Toyota began integrating the technology in 2021 for the bZ4X, Subaru Solterra (which shares Toyota's platform), and Lexus RZ. Aspen CFO Ricardo Rodriguez confirmed in September 2025 that these vehicles remain in volume production with PyroThin barriers.

European adoption is accelerating rapidly. Audi has awarded a multi-year contract for the next-generation A6 E-Tron platform based on the Premium Platform Electric (PPE) architecture. Porsche, working through manufacturing partner Valmet Automotive, will use PyroThin in the electric 718 series—the Boxster and Cayman EVs expected in 2026-2027. Scania, the commercial truck manufacturer within Volkswagen Group, has a production contract launching in late 2024.

Perhaps most strategically significant is the December 2023 award from Automotive Cells Company (ACC), the battery cell joint venture owned by Stellantis, Mercedes-Benz, and TotalEnergies' Saft division. This partnership positions PyroThin in vehicles spanning 15+ brands across Stellantis (Jeep, Ram, Fiat, Peugeot, Chrysler, Dodge, Alfa Romeo, Maserati, and others) plus Mercedes-Benz, with production ramping through 2026-2027.

Aspen has announced eight OEM awards total, including a 2025 contract with a leading U.S. automaker for a next-generation prismatic LFP platform targeting 2028 production. The company's East Providence, Rhode Island facility holds IATF 16949 automotive quality certification. A planned Georgia factory, backed by a $670.6 million DOE loan commitment, would expand capacity to serve more than two million vehicles annually.

Performance advantages justify the cost premium

At $300-$1,000 per vehicle depending on configuration, PyroThin represents a meaningful cost that automakers clearly consider justified given their adoption decisions. The value proposition rests on multiple factors beyond pure safety.

Compared to alternative thermal management solutions, PyroThin's combination of properties is unmatched. Mica sheets offer high-temperature resistance but are brittle, provide no mechanical absorption, and face ethical sourcing concerns. Silicone foam handles compression well but melts at thermal runaway temperatures. Ceramic barriers are rigid and cannot accommodate cell swelling. Traditional insulation materials require 40% greater thickness to achieve equivalent thermal protection to aerogel barriers—space that instead could hold additional battery cells.

According to Cabot Corporation testing data on aerogel materials, the technology enables 100°C improvement in insulation performance versus non-aerogel barriers at identical thickness. Weight savings approach 50% for equivalent thermal protection, and aerogel is 10-20x lighter than traditional thermal barrier materials. For range-sensitive EVs where every kilogram matters, these efficiencies compound.

The regulatory landscape increasingly favors premium thermal barrier materials. Current standards mandate five-minute evacuation windows; China's upcoming two-hour standard will require dramatically more robust solutions. PyroThin allows manufacturers to exceed these requirements rather than merely meet them—a meaningful advantage as battery energy densities increase and automakers push toward higher-performance chemistries with lower thermal stability.

The path forward for EV battery safety

Thermal runaway prevention in electric vehicles has evolved from an afterthought to a primary engineering challenge. The chemistry that enables high energy density—nickel-rich cathodes, graphite anodes, organic electrolytes—creates inherent thermal instability. As the Bolt and Kona recalls demonstrated, even rare manufacturing defects can trigger catastrophic failures that cost billions to remediate.

PyroThin addresses the fundamental physics of the problem. By creating thermal resistance lower than motionless air, maintaining protection at extreme temperatures, and improving performance under the compression that battery cycling demands, Aspen's aerogel technology transforms the cell-to-cell propagation pathway from a cascade trigger into a manageable containment challenge.

The 2024 Automotive News PACE Award and Innovation Partnership Award recognized this achievement specifically for the GM collaboration. With contracts spanning GM, Toyota, Audi, Porsche, Scania, and the Stellantis-Mercedes-Benz ACC venture, PyroThin has transitioned from promising technology to production-validated solution.

For the EV industry, the implications extend beyond individual vehicle safety. Consumer confidence, regulatory compliance, insurance costs, and brand reputation all depend on preventing the kind of battery fires that generate headlines and recalls. Aspen Aerogels' revenue growth—from $7 million in 2021 to over $230 million in EV thermal barriers by 2024—reflects how seriously automakers take this challenge. The aerogel barrier that is 97% air may prove to be one of the most consequential EV technologies of the decade.