Multistage emulsion polymerization, consisting of three main stages, the preparation of alkali-swellable seed latexes, core-shell polymerization, and a neutralization stage, was carried out to make hollow polymer particles. The key points for the recipe are lower monomer partitioning in the seed particles, a higher instantaneous conversion, monomer-starved condition, and particle growth based on heterocoagulation. Before neutralization, TEM micrographs showed that the composite particles have one region of low electron density at the center of each particle, which implies the formation of concentric core-shell particles comprised of a carboxylated polymethylmethacrylate core and polystyrene shell. The transition layer between the core and the shell polymers was found to have a thickness of about 30 nm. The formation of closed voids inside the particles after drying the neutralized latexes was confirmed based on the change of particle morphology using transmission and scanning electron microscopy. The collapse of the shell layer was also observed, and was attributed to insufficient shell strength. The undeformed spherical shape of freeze-dried latex particles established that the collapse occurred during the drying stage and was related to the osmotic pressure generated by the shrinkage of the swollen core. The collapse of the particles was effectively prevented by the incorporation of one more polymerization stage involving the crosslinking of the shell after neutralization. Model hollow polymer particles with void sizes ranging from 130 to 770 nm were prepared using a recipe including the incorporation of an intermediate shell layer between the hydrophilic polymer core and the outermost crosslinked polystyrene shell layer.