The radiative zone is the layer in a star where energy is transported outward by radiation. The thickness of the radiative zone depends on the star's mass, luminosity, and opacity. In general, the radiative zone is thinner in more massive and luminous stars, and thicker in less massive and less luminous stars.

For example, in the Sun, which is a main sequence star of average mass and luminosity, the radiative zone is about 0.7 solar radii thick. In comparison, the radiative zone in a red giant star, which is a more massive and luminous star, is only about 0.1 solar radii thick. On the other hand, the radiative zone in a white dwarf, which is a less massive and less luminous star, can be as thick as several solar radii.

The thickness of the radiative zone can also affect the star's overall evolution. For example, a star with a thick radiative zone is more likely to develop a convective envelope, which can lead to the star pulsating or even exploding as a supernova.