Comparison between spectra produced by a pure-metal plasma and an overionized plasma. Upper panel: in red, continuum-only spectrum of a typical overionized SNR (Si abundance set to 3, τ_rec = 10¹¹ s cm⁻³, kT_fin = 0.5 keV and kT₀ = 5 keV); in black, continuum-only spectrum of a typical pure-ejecta plasma in CIE (Si abundance set to 300 and kT = 0.5 keV). Both spectra are synthesized assuming an exposure time of 10⁸ ks. Lower panel: same as upper panel but assuming an exposure time of 100 ks and also including the line emission.