A method using safe and mild conditions to prepare water-core colloidosomes of a few micrometers in size is examined. Using poly(styrene-co-butylacrylate) colloidal particles of 180 nm in size, with a low-temperature glass transition of 30 or 42 degrees C, the self-assembly into micrometer-sized water-core polymer shell particles is demonstrated. The effect of oil phase type, surfactant and cosolvent, sintering time, and the method of transfer into an aqueous phase are all examined. The work demonstrates the production of water-core rigid-shell colloidosomes at low temperatures, between 35 and 65 degrees C.