A novel method to control coating thickness of microcapsules is reported for polymer microcapsules containing inorganic microparticles, in this case silica balloon. iron, silica balloon coated by TiO2 using gas-liquid cosolvency of supercritical carbon dioxide. A suspension of inorganic microparticles in carbon dioxide (CO2.) containing a cosolvent and dissolved polymer is sprayed through a nozzle to atmospheric pressure. The polymers are poly (styrene)-poly (methyl methacrylate)-poly (glycidyl methacrylate) triblock copolymer (PS-b-(PMMA-co-PGMA) NL W.=5,000), poly (methyl methacrylate) (PMMA; M. W. = 15, 000), poly (ethylene glycol) (PEG; M. W = 7,500), poly (L-lactic acid) (PLLA; NL W. = 5,000), and PEG-poly (propylene glycol) (PPG) PEG triblock copolymer (M, W. = 13,000). The solubilities of these polymers in CO2 increase significantly with the use of low molecular weight alcohols as cosolvents. After expansion, the particles do not tend to agglomerate, since the pure cosolvent is a nonsolvent for the polymer. The structure and morphology of the microcapsules were investigated by SEM with EPMA, TEM, laser diffraction particle size analysis, and optical microscopy. The thickness of the polymer coating about the silica balloon, and likewise, the mean particle diameter and particle size distribution could be controlled by changing the feed composition of the polymer.