A set of thermoplastic expandable microspheres was investigated with respect to their crosslinking density and expandable property. The crosslinking efficiencies of dipentaerythritol hexaacrylate in a set of thermoplastic expandable microspheres were measured. As expandable properties, expansion curves were measured by using a thermomechanical analyzer, and they also were shown by measuring the change of thickness of the coated compound consisting of ethylene-vinyl acetate copolymer resin emulsion and CaCO3 with thermoplastic microspheres on paper. In view of the expansion ratio and heat resistance, as crosslinking density, a swelling ratio of about 20-25 is needed to achieve optimum expansion without collapse and rupture of microspheres. (C) 2004 Wiley Periodicals, Inc.