Thermal conductivity is a measure of a material’s ability to conduct heat. It tells us how quickly and efficiently heat can pass through a material. When we talk about W/mK, we’re discussing watts per meter kelvin. This unit measures the heat transfer rate across a material with a thickness of one meter when there is a temperature difference of one kelvin. In simpler terms, a higher W/mK value means heat travels through the material more easily. This concept is central to designing anything that needs to manage heat, from electronics to buildings to automotive systems.
For engineers selecting thermal insulation materials, mica’s thermal conductivity is important, but it should be evaluated alongside operating temperature, dielectric performance, dimensional stability, and product construction. Mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K and is often specified where thermal resistance, electrical insulation, and high-temperature stability must work together. This guide covers mica W/m·K values, what drives the difference between muscovite and phlogopite, and how to specify the right mica material for EV battery, electronics, and high-temperature insulation applications.
What Is Thermal Conductivity? (W/m·K Explained)
Heat transfer happens in three ways: conduction, convection, and radiation. Thermal conductivity specifically describes conduction, the process by which heat moves through a material without the material itself moving. In a hot metal rod, for example, heat travels from the hotter end to the cooler end by the vibration and movement of particles within the metal.
The effectiveness of this heat transfer depends on the material’s atomic structure. Some materials, like metals, have free electrons that can move easily and carry heat along. Other materials, such as wood or plastic, generally lack mobile free electrons, which makes them poorer conductors.
The table below shows where mica falls relative to common reference materials. Note the gap between mica and structural metals. Mica is not used as a total thermal barrier; it is often specified where controlled heat transfer, electrical insulation, and high-temperature stability must work together.
| Material | Thermal Conductivity (W/m·K) |
| Air | 0.024 |
| Fiberglass insulation | 0.035–0.045 |
| Mica | ~0.3 through-thickness |
| Aluminum | commonly around ~200–240, depending on grade and temperature |
This is the range that matters for engineers specifying mica as a thermal insulator: it can help reduce direct metal-to-metal or metal-to-component heat transfer while still supporting controlled heat movement where the assembly design requires it.
Thermal Conductivity of Mica
Mica’s thermal conductivity is not a single number for every product form or application. It depends on the grade of mica, product construction, and the direction heat is traveling through it.
Sheet mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K. Muscovite mica is commonly used where strong dielectric performance is required at lower to moderate high-temperature ranges, with continuous service around ~500°C and intermittent exposure up to approximately 800°C. Phlogopite mica is typically selected for higher-temperature environments, with continuous service around ~700°C and intermittent exposure up to approximately 1000°C, depending on grade and construction.
That directional behavior can matter in mica sheet design because mica is a layered mineral material. Heat does not move through every direction of a mica sheet in the same way, so engineers can evaluate mica orientation, thickness, and construction to help manage heat flow through the assembly.
Among other insulation materials used at elevated temperatures, mica holds a distinct position:
| Material | Thermal Conductivity (W/m·K) | Temperature Performance Notes |
| Mica (muscovite) | ~0.3 through-thickness | ~500°C continuous service; intermittent exposure up to approximately 800°C, depending on grade and construction |
| Mica (phlogopite) | ~0.3 through-thickness | ~700°C continuous service; intermittent exposure up to approximately 1000°C, depending on grade and construction |
| Ceramic fiber blanket | ~0.05–0.35 | Conductivity rises with temperature; representative blanket data is ~0.13 W/m·K at 600°C and ~0.36 W/m·K at 1200°C for 128 kg/m³ material |
| Fiberglass | 0.035–0.045 | Conductivity generally rises as temperature increases; grade, density, and product construction affect performance |
| Aerogel | 0.012–0.024 | Temperature capability depends on the specific product formulation and construction |
Fiberglass and aerogel offer lower thermal conductivity, but thermal conductivity alone does not determine whether a material is suitable for high-temperature industrial insulation. Mica’s value comes from its combination of controlled thermal resistance, high-temperature stability, dimensional stability, and electrical insulation performance in a single material system.
Why Mica’s Thermal Conductivity Matters for Industrial Applications
EV batteries: In the context of automotive thermal runaway, managing heat inside a battery pack is a safety-critical design problem, not a comfort feature. Mica’s controlled thermal conductivity can help it function as a barrier between cells, helping slow heat transfer and limit propagation risk in the event of a cell failure, while supporting thin, fabricated formats for tight pack tolerances. This is why mica sheets and mica-based barrier materials are evaluated in battery pack designs where thermal propagation resistance is part of the design and validation process.
Electronics: High-density electronics need materials that separate components electrically while still allowing controlled heat movement rather than localized heat buildup. Mica’s dielectric performance, combined with its through-thickness thermal conductivity of approximately 0.3 W/m·K, can support use in insulating layers in power electronics, transformers, and heating elements, where electrical isolation and thermal performance must be evaluated together.
Aerospace: In the aerospace industry, components face high temperatures, temperature cycling, and tight material constraints. Mica’s high-temperature stability, combined with its electrical insulation performance and dimensional stability, makes it a specified material option in aerospace thermal and electrical insulation assemblies.
Foundry and steel: Kiln linings, furnace components, and molten-metal handling equipment all require insulation that performs consistently at sustained high temperatures. Mica’s thermal and dielectric performance can remain useful in temperature ranges where organic and many polymer-based insulators degrade, making it a practical material option in foundry and steel processing environments.
Muscovite vs. Phlogopite: Thermal Conductivity Comparison
Muscovite and phlogopite differ most by temperature capability and dielectric performance, so grade selection should be addressed early in the specification process.
Sheet mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K, but performance depends on grade, product construction, and heat-flow direction.
Muscovite is commonly used for electrical insulation applications where strong dielectric performance is required at lower to moderate high-temperature ranges, with continuous service around ~500°C and intermittent exposure up to approximately 800°C.
Phlogopite is typically selected for higher-temperature environments, with continuous service around ~700°C and intermittent exposure up to approximately 1000°C, depending on grade and construction.
For a full breakdown of where each grade fits, see [Muscovite or Phlogopite? Which Mica Is Best for Your Application].
How to Specify Mica Thermal Conductivity for Your Application
Getting the right mica grade and format for a thermal insulation application comes down to four questions:
- Temperature range: What is the continuous operating temperature, and what is the maximum intermittent exposure the material needs to withstand?
- Direction of heat flow: Does the application need heat managed along the sheet plane, reduced through the sheet thickness, or both in different zones of the same assembly?
- Thickness requirements: Thinner sheets can allow faster heat transfer, all else equal; thicker laminates can increase thermal resistance.
- Electrical insulation requirements: Many mica applications require dielectric performance alongside thermal performance, so the two specifications should be evaluated together.
Axim Mica custom-fabricates mica sheets, mica tapes, flexible mica composites, and 3D molded mica components around application-specific temperature, dielectric, dimensional, and installation requirements.
Specify mica around the thermal, electrical, and dimensional requirements of your application demands. [Contact Axim Mica] to discuss your project.
FAQ
What is the thermal conductivity of mica?
Sheet mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K. Actual performance can vary by mica grade, product construction, temperature, and heat-flow direction relative to mica’s layered structure.
Is mica a good thermal conductor or insulator?
Mica is a thermal insulator relative to metals. Sheet mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K, far below aluminum, which is commonly around ~200–240 W/m·K depending on grade and temperature. It can conduct more heat than air or dedicated low-conductivity insulation like aerogel. That middle position is what makes mica useful in applications needing electrical insulation, high-temperature stability, and some controlled heat transfer, rather than a total thermal barrier.
What is W/m·K?
W/m·K stands for watts per meter-kelvin, the SI unit for thermal conductivity. It measures how much heat, in watts, passes through one meter of a material when there is a one-kelvin temperature difference across it. Lower values generally mean slower heat transfer under the same conditions.
How does mica’s thermal conductivity compare to other materials?
Among common insulation materials, sheet mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K. This is higher than fiberglass insulation at ~0.035–0.045 W/m·K and aerogel at ~0.012–0.024 W/m·K, while overlapping with some ceramic fiber values depending on product form and temperature.
What sets mica apart is not low conductivity alone, but its combination of controlled thermal resistance, electrical insulation performance, dimensional stability, and high-temperature capability. Muscovite mica provides continuous service around 500°C, with intermittent exposure up to approximately 800°C, while phlogopite mica provides continuous service around 700°C, with intermittent exposure up to approximately 1000°C, depending on grade and construction.
Does mica type affect thermal conductivity?
Yes. Muscovite and phlogopite are both micas, but their temperature capability, dielectric performance, and product construction can affect how each material is specified. Sheet mica has a through-thickness thermal conductivity of approximately 0.3 W/m·K, with actual performance varying by grade, construction, temperature, and heat-flow direction.
Muscovite is commonly used where strong dielectric performance is required at lower to moderate high-temperature ranges, with continuous service around 500°C and intermittent exposure up to approximately 800°C. Phlogopite is typically selected for higher-temperature environments, with continuous service around 700°C and intermittent exposure up to approximately 1000°C, depending on grade and construction.
