AbstractThe adhesion between ammonium perchlorate filler and the polybutadiene rubber matrix was investigated. The aggregate composite was modified by surface pretreatment of the filler with various organofunctional silanes. For comparison, the adhesion of glass beads and glass powder, each coated with a fluorocarbon release agent, and carbon black were used as fillers in the cured polybutadiene matrix. Common testing methods used included the determination of Poisson's ratio, photographic analysis, and absorption of water. A new type of stress–strain analysis was introduced. Results closely agreed with established composite theory. The presence of methacryloxy‐ and amino‐functional silanes improved adhesion to the resin system. Epoxy‐ and vinyl functional silanes proved to be detrimental at the filler–rubber interface. A major function of the coupling agents appears to be to eliminate the weak boundary layer of surface moisture on the filler