Pressure as a function of radial position along an isentrope in the interior of our fiducial sub-Neptune with a fully miscible core. The envelope–core interface is at R/R_c = 1, where R_c is the radius of the interior exclusive of the outer hydrogen-rich envelope (the “core”). The planet total mass is 6 M_⊕ and has a bulk H₂ concentration of 2% by mass. The positions of the isobaric, isothermal phase diagrams in Figure 10 are shown for reference.