High amounts of silicon dioxide are readily incorporated into an emulsion polymerized elastomer by mixing an aqueous dispersion of silicon dioxide with a latex of the emulsion polymer and subsequently spray drying the mixture. Free flowing, fine-size (e.g., less than 500 micrometers) particles are produced with generally complete incorporation of silicon dioxide. The presence of the silicon dioxide permits rubbers with low gel and/or low Mooney viscosity to be spray dried whereas previously this could not be accomplished. Compared to conventional means of adding a silica to a bale rubber, the above powdered masterbatch gives shorter mixing times with lower power consumption with improved physical properties, such as tensile strength.