Diffuse dark matter (DM) mass fraction, f_d, in filaments. Different shades of purple and blue represent different radial zones around the filament spines. Histograms and solid lines show the differential and cumulative distributions of diffuse fractions over individual filaments, with the correspondingly coloured dotted vertical line giving the median fraction. The analogous distributions for the centre and outskirts of groups are shown in red and orange, respectively, while the dash-dotted green vertical line marks the average diffuse fraction of DM outside of groups or identified filaments. Most filaments are substructure dominated in their centre (low f_d), in contrast to groups.