The present invention relates to a composition comprising an aqueous dispersion of multistage polymer particles comprising a first and a second phase, wherein the first phase comprises structural units of a carboxylic acid monomer or a salt thereof, and a nonionic ethylenically unsaturated monomer; and wherein the second phase comprises a first and second polymer, wherein the first phase or the second phase first polymer or both comprise structural units of a high T_ghydrophobic monomer; and wherein the second phase second polymer comprises at least 80 percent structural units of styrene. The high T_ghydrophobic monomer is defined as being one or more of the following monomers: cyclohexyl methacrylate, isobornyl methacrylate, 4-t-butyl methacrylate, t-butylstyrene, orn-butyl methacrylate. The multistage polymer particles are useful as opaque polymers, which are used in pigmented coating formulations to reduce the load of TiO₂. The particles exhibit excellent collapse resistance and unusually low dry bulk density, and do not require acrylonitrile to achieve this desired combination of properties.