Thermal conductivity is defined as the amount of heat energy transferred per unit area per unit time through a unit thickness of a material, for a temperature gradient of one degree Celsius (or Kelvin) per unit length. The SI unit of thermal conductivity is Watt per meter-kelvin (W/(m·K)). The formula for thermal conductivity ($k$) is given by:

Where:

• $k$ is the thermal conductivity,
• $Q$ is the heat energy transferred,
• $A$ is the cross-sectional area through which heat flows,
• $L$ is the thickness of the material,
• $\Delta T$ is the temperature difference across the material.