Inferred posteriors for the most important internal structure parameters of TOI-396 b. The depicted parameters are the mass fractions of the inner core (w_core), mantle (w_mantle) and envelope layers (w_envelope) with respect to the total planet mass, and the mass fraction of water in the envelope (Z_envelope). The top row shows the results when assuming a water prior motivated by a formation of the planet outside the iceline (case A), while the bottom row uses a water prior compatible with a formation inside the iceline (case B). At the same time, we run models with three different compositional priors for the planetary Si/Mg/Fe ratios: stellar (purple, option 1), iron-enriched compared to the star (pink, option 2) and sampled using a uniform prior (blue, option 3). The dotted lines show the prior distributions, while the dashed vertical lines show the median values of the posteriors.