Planetary masses and radii of the known transiting exoplanets (values taken from the Transiting Extrasolar Planet catalogueue, TEP-Cat, which is available at http://www.astro.keele.ac.uk/jkt/tepcat/catalogue; Southworth 2010, 2011) with equilibrium temperature T_eq between 600 and 1000 K and host star radius between 0.6 and 1.5 R_⊙. Different lines correspond to different mass fractions of relatively cold hydrogen envelopes. The ice giants of the Solar System are displayed in filled black circles. TOI-1422 b is on the low-density envelope of planets with precise mass and/or radius estimations (σM_p/M_p ≤ 30%; σR_p/R_p ≤ 10%), one of the reasons that make it potentially valuable for transit spectroscopy.