From about 0.7 solar radii to 1.0 solar radii, the material in the Sun is neither dense nor hot enough to transfer the heat energy of the interior outward. As a result, thermal convection carries the heat to the surface as thermal columns carry hot material to the surface (photosphere) of the Sun. Once the material cools off at the surface, it plunges back downward to the base of the convection zone, to receive more heat from the top of the radiative zone. There is a bit of convective overshoot at the base of the convection zone, carrying turbulent downflows into the top layers of the radiative zone.