Elemental and X-ray fluorescence analyses were performed to determine the chemical compositions of insulator and jacket poly(vinyl chloride) (PVC) samples. In addition, differential scanning calorimetry (DSC) measurement was performed to determine their glass-transition temperatures (T-g) and melting points. The effect of additives on the two investigated samples, as well as on a pure PVC sample, was studied using Doppler-broadening energy spectra coupled with the slow positron beam technique. Significant variation in the S parameter as a function of positron implantation energy and depth from the surface to the bulk was observed in all samples. The S parameter increased at a very low positron energy (< 1 keV), saturated to about 6 keV, and then decreased up to 27 keV. The S parameter (Delta S) changed to the extent of the change in the breadth of the distribution of free-volume defects, which was larger in the jacket PVC sample, which had more additives, than in the insulator PVC sample. (c) 2006 Wiley Periodicals, Inc.