Thermal-runaway barrier materials: properties compared
Draft: values below are typical ranges compiled from manufacturer literature and are being checked against current datasheets. Do not use for design until this notice is removed.
Short answer: Fibre-reinforced silica aerogel has the lowest thermal conductivity of common barrier materials. Mica gives the best resistance to flame, particle jets and high voltage, but conducts more heat. Ceramic-fibre paper sits in between. Many production barriers therefore combine an aerogel or fibre core with mica or ceramic facings.
Comparison table
Ranges are typical published values. Test methods and temperatures differ between suppliers; always use the current datasheet for design. Scroll sideways on small screens.
| Material | k at ~25 °C, W/(m·K) | k at high temperature | Max. temperature | Density | Typical thickness | Compression behaviour | Electrical insulation |
|---|---|---|---|---|---|---|---|
| Silica aerogel blanket / pad (fibre-reinforced) | 0.015–0.025 | ≈0.035–0.05 at 400 °C; ≈0.05–0.09 at 500–600 °C | ≈650 °C continuous (unshielded); short exposures higher when faced | ≈70–300 kg/m³ | 1–5 mm (often 2–3 mm) | Compressible ≈10–30 %, partial rebound | Insulating; breakdown typically ≥3.5 kV per pad when encapsulated |
| Mica sheet / board (muscovite, phlogopite) | ≈0.2–0.6 (through-plane) | Stays ≈0.2–0.6 | Muscovite ≈500–600 °C; phlogopite ≈700–800 °C continuous; higher short-term | ≈1,800–2,350 kg/m³ (bonded sheet) | 0.2–2 mm | Essentially rigid | Excellent; typically ≥20 kV/mm at room temperature |
| Ceramic-fibre / bio-soluble fibre paper | ≈0.035–0.05 | ≈0.06–0.12 at 400 °C; ≈0.08–0.16 at 600 °C | Fibre rated ≈1,100–1,400 °C | ≈140–290 kg/m³ | 0.8–6 mm | Some initial compression; limited rebound | Good when dry; binder burns out at ≈250–450 °C |
| Intumescent / endothermic barrier sheet | ≈0.05–0.3 (before activation) | Not comparable: works by expanding or absorbing heat | Activates ≈150–200 °C; char stable to ≈1,000 °C | ≈300–1,500 kg/m³ | 0.5–3 mm between cells | Varies; expansion is irreversible | Depends on formulation: graphite-based chars become conductive |
| Silicone foam / compression pad | ≈0.06–0.15 | Polymer pyrolyses above ≈350 °C; ceramifying grades form a silica char | ≈200 °C continuous; fire-blocking grades survive short flame exposure | ≈190–800 kg/m³ | 1.5–6 mm | Best reversible compression and low compression set | Good |
| Phase-change material (PCM) plate | ≈0.2 (paraffin) to 3–15 (graphite composite) | Not applicable: decomposes above ≈200–300 °C | Melts at ≈25–70 °C; organic types unstable above ≈200 °C | ≈760–1,700 kg/m³ | 2–6 mm | Rigid | Paraffin insulates; graphite composites conduct |
| Composite barrier (aerogel or fibre core + mica / film facing) | ≈0.015–0.03 (aerogel core) | ≈0.04–0.06 at 500 °C (aerogel core); higher for fibre core | Facing survives short exposures ≈1,000 °C+ | ≈150–300 kg/m³ | 0.5–6 mm (often 1–3 mm) | Core compresses ≈10–30 % | Set by the mica or polymer facing |
Silica aerogel blanket / pad (fibre-reinforced)
Silica aerogel trapped in a glass- or ceramic-fibre mat. Its nanoporous structure suppresses gas conduction, giving the lowest thermal conductivity of the common barrier materials at room temperature and a clear advantage at a few hundred °C. Most battery grades are encapsulated in a film or faced with mica to control dust and add electrical and abrasion resistance.
Strengths
- Lowest thermal conductivity of common barrier materials, so thin layers are effective
- Light and compressible, so it can double as a compression pad between prismatic or pouch cells
- Widely qualified in production EV packs
Limitations
- The silica network can sinter and lose its low conductivity above roughly 650–800 °C if not shielded
- Unencapsulated material sheds dust
- More expensive per square metre than mica or ceramic-fibre paper
Example commercial products
- PyroThin (Aspen Aerogels, USA)
- Thermal Blade (JIOS Aerogel, Singapore / Korea)
- Aerogel battery pads (IBIH Advanced Materials, China)
- Aerogel battery insulation (Nano Tech Co. (纳诺科技), China)
Listing is not an endorsement and is not paid for. See disclosures.
Sources
Mica sheet / board (muscovite, phlogopite)
Mica paper bonded with silicone resin into flexible sheet or rigid board. It insulates heat about ten times worse than aerogel but is very hard to burn through, resists the abrasive jet of hot particles from a venting cell, and keeps high dielectric strength at temperature. It is the standard material for pack lids, busbar shields and the facing layer of composite barriers.
Strengths
- Very high dielectric strength, retained at elevated temperature
- Resists flame burn-through and particle erosion
- Low cost and mature supply chain
Limitations
- High density and much higher thermal conductivity than aerogel
- Rigid: cannot absorb cell swelling on its own
Example commercial products
- Mica thermal runaway barriers (Elmelin, UK)
- COGEMICANITE thermal runaway shields (Cogebi, Czech Republic)
Listing is not an endorsement and is not paid for. See disclosures.
Sources
Ceramic-fibre / bio-soluble fibre paper
Paper made from alumina-silica refractory fibres or alkaline-earth silicate (bio-soluble) fibres with a small organic binder. It survives far higher temperatures than aerogel at low cost, but insulates less well at the temperatures that matter for propagation.
Strengths
- Very high temperature resistance
- Low cost and light weight
- Easy to die-cut and laminate with mica
Limitations
- Higher conductivity than aerogel at 400–600 °C
- Organic binder burns off on first heating, releasing smoke
- Refractory ceramic fibre (RCF) has health classifications in some markets; bio-soluble grades avoid this
Example commercial products
- Superwool EST range (Morgan Advanced Materials, UK)
- FyreWrap LiB papers (Alkegen (formerly Unifrax), USA)
Listing is not an endorsement and is not paid for. See disclosures.
Sources
Intumescent / endothermic barrier sheet
Active materials. Intumescent sheets swell into an insulating char when heated, filling gaps and adding thickness. Endothermic sheets absorb heat by releasing chemically bound water. Both buy time rather than offering a fixed thermal resistance.
Strengths
- Thin when cold; insulation increases in a fire
- Endothermic types delay temperature rise of the protected cell
- Expansion seals gaps against hot gas
Limitations
- Single use: the reaction is irreversible
- Expandable-graphite chars conduct electricity unless laminated with a dielectric
- Expansion force can load the neighbouring cells
Example commercial products
- Thermal runaway barrier materials (3M, USA)
Listing is not an endorsement and is not paid for. See disclosures.
Sources
Silicone foam / compression pad
Closed-cell or syntactic silicone foams used mainly to manage cell swelling and hold stack pressure. Fire-rated and ceramifying grades add some thermal-runaway protection, often in combination with a mica or aerogel layer.
Strengths
- Excellent long-term compression behaviour for cell breathing
- Seals and gaskets well
- UL 94 V-0 grades are common
Limitations
- Higher conductivity than aerogel
- Continuous service limited to about 200 °C
- Releases volatiles when it decomposes
Example commercial products
- ProCell EV firewall and BISCO silicones (Rogers Corporation, USA)
- ELASTOSIL battery protection silicones (Wacker Chemie, Germany)
Listing is not an endorsement and is not paid for. See disclosures.
Sources
Phase-change material (PCM) plate
Plates that absorb heat while melting, used to smooth temperature peaks in normal operation. They are not fire barriers: organic PCMs are flammable and graphite-filled composites conduct heat toward neighbouring cells once the latent heat is used up.
Strengths
- Large latent heat buffers short temperature spikes
- Can reduce cooling-system demand
Limitations
- No protection once melted
- Organic PCMs add fuel in a fire
- Graphite composites conduct heat and electricity
Sources
Composite barrier (aerogel or fibre core + mica / film facing)
Laminates that put a low-conductivity core (aerogel or fibre) between tougher facings (mica, ceramic paper, polyimide or PET film). This is the dominant format in current production because it covers all four barrier jobs: insulation, compliance, dielectric strength and burn-through resistance.
Strengths
- Balances insulation, compression, dielectric and burn-through performance
- Dust-free when fully encapsulated
Limitations
- Higher cost than single materials
- Thicker and heavier than bare aerogel
Example commercial products
- AlkeGel aerogel composites (Alkegen, USA)
- Superwool EST mica-faced papers (Morgan Advanced Materials, UK)
Listing is not an endorsement and is not paid for. See disclosures.