Water mass fraction vs planet radius. The markers are colour-coded according to the H/He mass fraction for the synthetic analogues of HIP 29442 b, c, and d. The large points are the synthetic analogues of planet b, c, and d considering the full planetary system, while the transparent, smaller points in the background are the synthetic analogues for the single-planet system of each planet. The areas shaded in green, pink and purple respectively indicate the 1σ confidence interval of the observational radius for each planet, while the areas shaded in blue are the water mass fractions inferred from the internal structure modelling (model A1 with stellar Si/Mg/Fe prior and assuming a formation outside the iceline). The dashed lines indicate the 2σ and 3σ values of the respective distributions. Synthetic planets that fall in the shaded areas are good synthetic matches for the observed planets.