Black shells and naked shells.

We study the null surfaces that appear during the gravitational collapse of a spherically symmetric thin shell. Considering the horizon properties of the null surfaces, we show that there can be three different structures: Black shells that can have either one or two horizons and naked shells, in which the end state of the evolution corresponds to a naked singularity. We investigate the gravitational and thermodynamic properties of these configurations and show their consistency from a physical viewpoint.