The concept of microvoid toughening of polymers has been proposed by several investigators. This investigation illustrates the similarities between the function of rubber particles in rubber-toughened plastics with that of microvoids. While previous researchers created microvoids within polymeric materials by means of non-adhering particles, our novel approach is based on using hollow plastic micro-spheres to generate holes. An epoxy polymer is used as a model polymer matrix. The results of this investigation show that hollow plastic particles toughen the epoxy resin in the same manner as rubber particles. Surprisingly, mechanical characterization of modified blends revealed that the use of hollow plastic micro-spheres provides greater yield strength than that of similar blends with equivalent rubber content.