Filament volume fractions filled by oxygen and O VII. Left panel: volume filled by oxygen (turquoise line) and O VII (dashed purple line) at a given number density within the IGM in Bisous filaments, as a fraction of total Bisous volume. Right panel: fraction of the volume above a given number density n (cm⁻³) for oxygen (turquoise line) and O VII (dashed purple line) within Bisous outside haloes normalised by the total Bisous volume. The grey shaded area indicates the assumed observational limits, for a path between 1 Mpc (log n ≈ −9) and 10 Mpc (log n ≈ −10) along the line of sight.