Hollow mesoporous silica spheres that are highly defined in shape and size (see Figure) are prepared using a poly(ethylene oxide)poly(propylene oxide)-poly(ethylene oxide) [PEO-PPO-PEO] block copolymer based emulsion as the template, and sodium silicate as the silica source. The wall structure of the particles depends on the reaction temperature and can be monitored using small-angle X-ray scattering, solid-state NMR spectroscopy, and cryo-transmission electron microscopy.