The heat capacity of metallic systems follows the Debye model, which indicates that in three dimensions, heat capacity is proportional to the temperature cubed. While this relationship holds for the lattice contribution in metals, there is an additional, smaller contribution from free electrons that becomes significant only at very low temperatures. Therefore, in certain temperature ranges, the cubic relationship is applicable to metals. The discussion emphasizes that the Debye model is relevant for understanding heat capacity in metallic systems. Overall, the findings clarify how heat capacity behaves in metals compared to non-metallic systems.