Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, $$\rho $$ = Density of substance, S = Specific heat and k = Thermal conductivity)

Thermal Diffusivity is defined as the ratio of heat conducted to the heat energy stored per unit volume of a material.
The thermal conductivity of a substance divided by the product of its density and its specific heat capacity.
Thermal diffusivity of a substance is given by $${\text{h}} = \frac{{\text{k}}}{{\rho {\text{S}}}}$$
(Where h = Thermal diffusivity, $$\rho $$ = Density of substance, S = Specific heat and k = Thermal conductivity)