Thermal Diffusivity

Thermal diffusivity corresponds to the speed of heat propagation in a material. It is therefore expressed in m²/h. Physically, thermal diffusivity expresses a body’s ability to transmit heat rather than absorb it. In fact, the lower the thermal diffusivity value, the longer the heat will take to pass through a material thickness, and the longer the time taken by the heat front to travel the distance between the two faces of the material.
The thermal diffusivity determines the thermal inertia of a material: its predisposition to keep its initial temperature for a long time when a disturbance of this thermal equilibrium appears. If the perturbation brings it to a new equilibrium temperature, this thermal inertia represents the time taken for this new equilibrium point to be reached.

Diffusion is not a parameter that we can measure directly. It is obtained by measuring the thermal conductivity and the emissivity.