Heat capacity is the ability of a material to store heat, higher the heat capacity higher the amount to heat stored by the material. Heat transfer usually varies inversely with heat capacity, i.e heat transfer will decrease with increase in heat capacity and vice versa. Thermal diffusivity is the ratio of thermal conductivity to the heat capacity, it says how fast (or slow) heat is transferred inside a material. Usually thermal diffusivity is directly proportional to the heat transfer rate, since heat capacity appears on the denominator, heat transfer is inversely proportional to the heat capacity.
