The impact of temperature on the filterability of synthetic sludge, using the capillary suction time (CST) test, was investigated. The CST was measured at five temperatures, six total suspended solid (TSS) concentrations, and two funnel geometries. The results were not consistent with the hypothesis that the CST declines at higher temperatures through the lowering of the sludge viscosity. The impact of temperature on the results of CST tests was moderated by other physicochemical properties of the sludge (desorptivity, particle size composition, and chemical constituents) associated with the efficiency of flocculation.