How Thick Should Aerogel Insulation Be Between EV Battery Cells?

If the aerogel barrier is too thin, heat from a failing cell can reach its neighbor too quickly; if it is unnecessarily thick, the pack loses valuable cell volume, adds cost, and can alter cell compression.

There is no universal aerogel thickness for EV batteries—the correct value must be selected from cell chemistry, thermal-runaway energy, available gap, compression, allowable protected-side temperature, and module validation results. For prismatic and pouch cells, engineered barriers are often only a few millimeters thick, but the final value must be proven in the actual battery architecture.

Is There a Standard Aerogel Thickness for EV Battery Cells?

Using a fixed rule such as “2 mm aerogel is enough for every battery” can under-protect high-energy cells or waste space in a lower-risk module.

The correct solution is to define thickness from the required thermal resistance under the actual compressed condition. Cell format, chemistry, stored energy, spacing, vent direction, compression force, barrier construction, and allowable temperature on the neighboring cell all influence the result.

Aspen Aerogels states that its automotive cell barriers are engineered for specific targets including thermal conductivity, thickness, and compression response, reinforcing that barrier thickness is an application-dependent design parameter rather than a universal number.^[1]

Can a 2–3 mm Aerogel Barrier Be Enough?

Quoting a successful 2–3 mm test result without considering cell size, compression, heat paths, and venting can create false confidence in a completely different battery pack.

A few millimeters can be technically viable in some prismatic or pouch-cell designs, but only when the complete module test confirms the required propagation delay. Thickness cannot be separated from material formulation and compression state.

Aspen published one mini-module example using a 2.35 mm PyroThin barrier compressed to about 50% strain between two 62 Ah prismatic cells. In that specific test, the neighboring cell did not enter thermal runaway, but Aspen also notes that the mini-module isolated some secondary heat paths found in a real pack.^[2]

That 2.35 mm result is therefore a useful engineering example—not a universal EV specification.

How Does Compression Change the Required Thickness?

A barrier selected only by its uncompressed thickness may perform very differently once cells swell and the module compresses the material throughout vehicle life.

The solution is to evaluate both beginning-of-life and end-of-life compressed thickness and thermal performance. Prismatic and pouch cells can change dimension during cycling, so the barrier may also act as a compression pad while maintaining thermal resistance.

Aspen specifically identifies mechanical performance, compression fatigue, and thermal conductivity under compression as critical design factors for cell-to-cell barriers.^[3]

What Factors Determine Aerogel Thickness?

Selecting thickness from thermal conductivity alone ignores other heat paths and mechanical constraints that can dominate real thermal-runaway propagation.

Engineers should evaluate the complete cell-to-cell interface before freezing the barrier thickness. The most important inputs are shown below.

Why Not Simply Use a Thicker Aerogel Barrier?

Oversizing every cell barrier can reduce pack energy density, increase module dimensions and cost, and interfere with the intended cell compression system.

The correct solution is to use the minimum validated construction that meets the thermal-propagation and mechanical requirements with adequate design margin. In high-volume EV packs, even an additional fraction of a millimeter repeated across dozens or hundreds of cell interfaces can materially affect pack dimensions.

This is one reason aerogel is attractive for cell-to-cell barriers: manufacturers can engineer very high thermal resistance into relatively thin, lightweight structures.^[4]

Does Cell Chemistry Change the Required Aerogel Thickness?

Using the same barrier design for LFP, NMC, and other cell chemistries can overlook major differences in thermal-runaway behavior, cell energy, venting, and pack architecture.

The barrier should be tuned to the actual cell chemistry and trigger-cell behavior. Aspen notes that its cell barriers are designed for multiple chemistries, including LFP, NMC, and emerging solid-state systems, with thickness and stiffness profiles optimized for specific applications.^[5]

Chemistry is important, but it is not the only parameter. Cell capacity, geometry, state of charge, spacing, compression, cooling, and neighboring structures can materially change propagation behavior.

Should Aerogel Thickness Be Selected Before Module Testing?

Freezing production thickness from a material datasheet alone can lead to expensive redesign if module-level tests reveal conductive, radiative, or vent-gas heat paths that were not represented by the coupon test.

Use material calculations and cell-level testing to define a starting thickness, then validate the complete construction at module or pack level before serial release. A real battery contains tabs, busbars, cooling plates, compression structures, gaps, fasteners, insulation, and vent paths that can bypass the primary cell-face barrier.

Aspen similarly states that battery modules and packs are complex systems and that there is no one-size-fits-all test for cell-barrier performance through end of life.^[3]

How Does Aerogel Thickness Affect Busbars and Battery Wiring?

Increasing cell-barrier thickness without checking the surrounding electrical packaging can change module stack dimensions and place additional stress on busbars, sensing wires, connectors, or high-voltage harness routing.

The correct solution is to review aerogel thickness together with the electrical interconnection system. Changes in cell spacing can alter busbar geometry, BMS sensing-wire length, connector position, insulation clearance, and the routing of high-voltage cables around the module.

For this reason, a thermal-barrier change should not be treated as an isolated material substitution. Cell spacing, compression, mica insulation, busbars, silicone pads, BMS wiring, and HV harness interfaces should be checked together before tooling is frozen.

Need to Define an Aerogel Cell Barrier?

For an engineering review, prepare the cell chemistry, capacity, cell dimensions, available gap, compression requirement, target thickness range, vent direction, thermal-propagation requirement, module CAD, and surrounding busbar or wiring layout.

A sample evaluation should confirm both thermal performance and compressed mechanical behavior before the final production thickness is released.

FAQ

What Is a Typical Aerogel Thickness Between EV Battery Cells?

There is no universal thickness. Engineered cell barriers can be only a few millimeters thick, but the final value depends on the material, cell design, compression, and required thermal-propagation performance.

Is 2 mm Aerogel Enough Between Battery Cells?

It may be sufficient in some designs and inadequate in others. Thickness must be validated using the actual cell chemistry, energy, compression, heat paths, and module architecture.

Does Compressing Aerogel Reduce Its Thermal Protection?

It depends on the aerogel construction. Automotive cell barriers should be characterized under their actual compression state because mechanical strain changes thickness and can influence thermal behavior.

Is Thicker Aerogel Always Safer?

No. More thickness may improve thermal resistance but can reduce pack energy density, alter cell compression, increase cost, and affect busbar or wiring geometry.

Should Aerogel Be Tested at Cell or Module Level?

Both can be useful. Cell-level tests help screen barrier performance, but module- and pack-level validation is important because additional heat-transfer and vent-gas paths exist in the complete battery system.

15-Year Automotive Battery and Wire Harness Perspective

Based on 15 years of automotive component and wire harness experience, I would never specify an aerogel barrier simply as “2 mm” or “3 mm” before understanding the battery stack.

The correct thickness is the minimum validated construction that controls cell-to-cell heat transfer while still meeting compression, packaging, busbar, sensing-wire, and high-voltage routing requirements. In an EV battery pack, thermal materials and electrical interconnections must be designed together.

Authoritative References

[1] Aspen Aerogels — PyroThin Aerogel Cell-to-Cell Thermal Barriers

[2] Aspen Aerogels — Cell-to-Cell Thermal Propagation Mini-Module Testing

[3] Aspen Aerogels — Thermal Barrier Design, Compression and Validation

[4] Aspen Aerogels — Thermal Runaway Propagation and Cell-to-Cell Barriers

[5] Aspen Aerogels — EV Battery Thermal Barrier Applications