Radius as a function of mass for a set of well-studied ND planets from the TEPCat catalogue. The solid curves show compositional bi-layer models from Zeng et al. 2016, ranging from 100% iron worlds to 100% water planets. The labels are colour-coded to represent the respective model. The dashed line models are taken from (Zeng et al. 2019), showing 2% and 5% H₂ envelopes at 1000 K and distinct core compositions.