Cofilin binds less efficiently to larger filament bundles. Fluorescence intensity of cofilin, normalized by the amount of F-actin, bound after 8 min after cofilin introduction in the “open chamber,” on segments of typically 4 µm of fascin-induced filament bundles of average size 3 (±0.8, SD, n = 8 segments) and 10 (±4, n = 10 segments) filaments. The large dots represent the median value of each population.