Planet radius as a function of planet mass along with lines of constant density from (Zeng et al. 2019). The gray-shaded region indicates planets with iron content exceeding the maximum value predicted from models of collisional stripping (Marcus et al. 2010). Confirmed USP planets are shown with bold foreground points, and other confirmed exoplanets from the NASA Exoplanet Archive are shown with the faint purple points. TOI-2431 b is shown in red. We only show systems with better than 3σ mass and radius constraints.