Synthesis in confined spaces: A simple route for designing and controlling the size of uniform zeolite nanocrystals (60–500 nm) uses the voids between monodisperse polymer spheres in an aqueous medium as nanoreactors. The crystal size is controlled by the content and diameter of the recyclable polymer spheres. The picture shows zeolite β nanocrystals (60 nm) with their X-ray diffraction (XRD) pattern (inset).