Sedimentation is often a problem in electrorheological (ER) fluids featuring solid particles suspended in a low-density hydrocarbon oil. This problem was addressed by synthesizing particles comprising silica microballoons coated with PVAL using a salt-induced coacervation process. The ER performance of the fluids based on these particles was equivalent to prototypical commercial fluids, both with respect to current leakage and shear stress under steady simple shear flow. For comparing diverse fluids as to these practical characteristics, a dimensionless ER effectiveness number, Er, was proposed : Er = sigma(gamma) over dot /EJ where sigma is the shear stress, (gamma) over dot, is the shear rate, E is the electric field, and J is the current. The resulting uniform coatings were also found to impart a degree of resistance to breakage.