Based on the spatiotemporal modulation of the thermal conductivity and volumetric heat capacity, we propose a thermal diode characterized by the rectification of conductive heat currents. By transforming the Fourier's law for the heat flux and the diffusion equation for the temperature into equations with constant coefficients, it is shown that: (i) the rectification effect is generated by the simultaneous wave-like modulation of both thermal properties, such that it disappears in absence of any of them. (ii) The rectification factor can be optimized and tuned by means of the speed and phase difference of the variations of the heat capacity and thermal conductivity. High rectification factors, greater than 86%, are obtained. The proposed thermal diode can open a new vista for developing different types of thermal wave logic components.