The velocities of longitudinal, transverse, and leaky surface skimming compressional waves (LSSCW) of polyvinylchloride composite materials were measured as a function of the particle concentration. The mica and calcium carbonate (CC) particles were used as additives. The longitudinal and transverse velocities for the PVC/mica composite increased with the concentration of the mica. In the case of the PVC/CC composite, the transverse velocity increased with the concentration of the CC particle, but the longitudinal velocity was independent of the concentration. The LSSCW velocity for the polyvinylchloride matrix did not change in each composite. The partial specific volume and the partial specific adiabatic compressibility of each particle dispersed in polyvinylchloride were evaluated from sound velocity and density data. The compressibility of the boundary layer around the particles was estimated. The thickness of the boundary layer around the mica particle was estimated. For the PVC/CC composite, on the other hand, a softer phase than the PVC matrix was formed around the CC particle because the compressibility of the boundary layer was larger than that of the PVC matrix. (c) 2005 Wiley Periodicals, Inc.