In static conditions, increasing fibrinogen γ′ levels within the (patho)physiological range increase clot density and reduce clot porosity. (A) Clots were formed under static conditions for purified experiments with 3%, 10%, and 30% fibrinogen γ′ in the presence (n = 3) or absence (n = 3) of FXIII. In parallel, clots were formed in patient samples (low γ′, n = 41; normal γ′, n = 45; high γ′, n = 33) with similar percentages of fibrinogen γ′. Clots were spiked with fluorescently labeled fibrinogen and viewed with a laser-scanning confocal microscope. Scale bar, 25 μm. (B) Clot density was quantified by calculating the number of fibers per 100 μm. (C) Permeation assays were carried out to calculate the porosity of clots. Data are mean ± SD. *P < .05, **P < .01, ***P < .001, ****P < .0001; 1-way ANOVA followed by Tukey’s multiple-comparisons test.