Mass range of heavy elements in the core (M_c) and in the envelope (M_Z,env) consistent with all observational constraints, for different numbers of layers, for Jupiter (bottom right) and Saturn (upper left). The open dots at the upper left of each region correspond to the homogeneous interior models. As the number of semiconvective layers increases, the efficiency of convection decreases, and the heavy element mass fraction increases to counteract the radius increase induced by the planet’s higher internal temperature. The metals initially present in the core are then redistributed within the envelope. For Jupiter, solutions with no core at all (M_c = 0) can be found for the non adiabatic models (red dots).