Thermal conductivity (symbol λ, unit W/(m·K)) indicates how well a material transports heat by conduction. For orientation: copper conducts excellently at 401 W/(m·K), steel is around 50, plastics around 0.2 and insulation materials such as mineral wool around 0.04 W/(m·K). Between the best and the worst technical heat conductor there is thus a factor of more than 10,000. Electrical insulating materials, such as the insulation materials GOBA processes, sit at 0.1 to 0.3 W/(m·K), in the range of plastics. On this page you will find the thermal conductivity of common metals, building materials, plastics and electrical insulating materials as tables, along with the unit, the formula and the most important influencing factors.
How is thermal conductivity measured?
Unit of thermal conductivity
The unit is watts per metre and kelvin (W/(m·K)). It indicates how much thermal energy is transported through a one-metre-thick material layer at a temperature difference of one kelvin. In the construction sector, the same value is known as the lambda value, and English-language data sheets frequently use the symbol k instead of λ.
Measurement methods for thermal conductivity
- Laser flash method: a laser pulse heats the surface, and the temperature rise on the back is measured.
- Hot wire method: a wire embedded in the material is heated by electric current.
- Plate methods: the amount of heat conducted through a material sample is measured directly.
Thermal conductivity table: materials at a glance
The table shows typical values at room temperature, sorted from the best to the worst heat conductor. Values may vary depending on purity, density and moisture:
| Material | Thermal conductivity (W/(m·K)) |
|---|---|
| Diamond | approx. 2,000 |
| Copper | 401 |
| Aluminium | 237 |
| Steel (unalloyed) | approx. 50 |
| Stainless steel | approx. 15 |
| Concrete | approx. 2.1 |
| Glass | approx. 0.8 |
| Water | 0.6 |
| Plastics (unfilled) | 0.15 to 0.35 |
| Wood (spruce) | approx. 0.13 |
| Mineral wool | 0.035 to 0.045 |
| Polystyrene foam (EPS) | 0.03 to 0.04 |
| Air (still) | 0.026 |
| Aerogel | 0.015 to 0.02 |
How does the thermal conductivity of various metals differ?
Comparison of the thermal conductivity of common metals
The following table shows the thermal conductivity of important metals at room temperature:
| Metal | Thermal conductivity (W/(m·K)) |
|---|---|
| Silver | 429 |
| Copper | 401 |
| Gold | 317 |
| Aluminium | 237 |
| Zinc | 116 |
| Brass | approx. 120 |
| Nickel | 91 |
| Iron | 80 |
| Tin | 67 |
| Steel (unalloyed) | approx. 50 |
| Lead | 35 |
| Titanium | 22 |
| Stainless steel (304) | approx. 15 |
Metals with particularly high thermal conductivity
Silver is the best metallic heat conductor at 429 W/(m·K), but for cost reasons copper (401 W/(m·K)) is almost always used in technology, for example in heat sinks, heat exchangers and copper foils. Aluminium reaches 237 W/(m·K) and scores wherever weight matters, for example in lightweight cooling systems.
Metals with low thermal conductivity and their applications
- Lead (35 W/(m·K)) is used, among other things, in radiation shielding.
- Iron (80 W/(m·K)) conducts considerably worse than copper or aluminium.
- Stainless steel (approx. 15 W/(m·K)) is the poorest common metallic heat conductor, ideal for cookware handles and thermal decoupling in mechanical engineering.
Which factors influence the thermal conductivity of metals?
Properties of metals and their effects
Metals consist of a crystal structure with freely movable electrons. These free electrons are responsible for the high thermal conductivity of metals, as they transport heat efficiently. This is why good electrical conductivity in metals almost always goes hand in hand with good heat conduction.
Temperature dependence of thermal conductivity
With rising temperature the thermal conductivity of most metals decreases, since the increased lattice vibration of the atoms hinders the transport of heat by electrons. Table values therefore always apply to a specific temperature, usually 20 °C.
Influence of alloys on thermal conductivity
Alloys reduce the thermal conductivity compared to pure metals, because foreign atoms restrict the mobility of the electrons. The jump from pure iron (80 W/(m·K)) to stainless steel (approx. 15 W/(m·K)) shows the magnitude of this effect.
Thermal conductivity of electrical insulating materials
Electrical insulating materials are meant to block current, but in many applications they must dissipate heat at the same time, for example in electric motors, transformers and power electronics. Exactly this trade-off determines the material selection, because most organic insulating materials lie between 0.1 and 0.3 W/(m·K). Typical guide values from the data sheets of the materials we process:
| Insulating material | Thermal conductivity (W/(m·K)) |
|---|---|
| Polyimide film (e.g. Kapton) | approx. 0.12 |
| Aramid paper (e.g. Nomex) | approx. 0.14 |
| Pressboard (dry) | approx. 0.17 |
| Polyester film (PET) | approx. 0.2 |
| Vulcanized fibre | approx. 0.2 |
| PTFE | approx. 0.25 |
| Mica / mica composite | approx. 0.3 to 0.7 |
| Thermally conductive compounds and films | 1 to 10 |
In practice, what counts for heat dissipation is less the λ value alone than the thermal transmittance of the entire insulating layer, that is λ divided by the material thickness. A 0.05 mm thin polyester film lets more heat through than a 0.5 mm thick layer of the same material, despite its low thermal conductivity. It is therefore worth not choosing the material thickness larger than the electrical design requires. For thermally highly stressed applications, we advise you on the material choice between standard films, high-temperature insulation and thermally conductive special solutions, matching the required insulation class.
Why is thermal conductivity important in construction?
Significance for thermal protection in buildings
Materials with low thermal conductivity such as mineral wool or polystyrene foam serve as thermal insulation and reduce the energy consumption of buildings. The lower the lambda value, the thinner the insulation layer may be for the same insulating effect.
Applications of metals with high thermal conductivity
Metals with high thermal conductivity are used for heat distribution, for example in underfloor heating and radiators.
Use of metals with low thermal conductivity
Low-conductivity metals serve as protective layers in fire protection structures and as thermal barriers.
How is thermal conductivity calculated in practice?
Formula for calculating thermal conductivity
The heat flow through a material follows the relationship: q = λ × (ΔT / Δx), where q is the heat flow in watts per square metre, ΔT is the temperature difference in kelvin and Δx is the material thickness in metres. A calculation example: at a temperature difference of 10 K, 10,000 watts per square metre flow through a 0.2 mm thick polyester film (λ = 0.2 W/(m·K)), but only 1,300 through an air layer of the same thickness.
Relationship with other thermal properties
- Heat capacity: the storage capacity for thermal energy
- Density: higher density often correlates with better heat conduction in solids
- Thermal diffusivity: the speed of heat propagation in the material
Which applications use the thermal conductivity of metals?
Use in electronics and electrical engineering
In computer processors, heat sinks and LEDs, high thermal conductivity is decisive for heat dissipation and reliable operation. Thin insulating films often sit between heat sink and component, which must separate electrically and couple thermally.
Applications in heat engineering and energy efficiency
Heat exchangers, solar systems and heating systems use materials with high thermal conductivity for efficient heat transport.
Use in industry and production
In the automotive industry and in mechanical engineering, materials with specific thermal conductivity are used to minimise thermal stresses, from battery insulation to motor windings.
GOBA conclusion: thickness governs heat transmission
Among electrical insulating materials the λ values sit close together: polyimide film at around 0.12, aramid paper at 0.14, polyester film at 0.2 W/(m·K). The difference inside the component comes from thickness. A 0.05 mm polyester film passes more heat than a 0.5 mm layer of the same material. So calculate with λ divided by material thickness and set the thickness to the minimum the electrical design requires. Every additional tenth of a millimetre traps loss heat inside the component. Where that heat path is not enough, thermally conductive films at 1 to 10 W/(m·K) take over, which we supply as insulating material with defined characteristics.
