Spectral energy distribution of I Zw 1 derived from the 2015 broadband observations. The best-fitting model (dotted red line) of the UV and optical data points (red diamonds) consists of a disc black body (solid red line), a stellar light component (green line), and a custom extinction curve. The reddening-corrected data and model are shown as well. The disc black body component is connected to the continuum model of the EPIC-pn spectrum (Rogantini et al. 2022, blue line) to form the SED (yellow curve). The observationally covered bands are depicted with the grey-shaded areas.