AbstractThe stabilizing action of calcium‐zinc stearate and pentaerythritol systems in PVC cannot only be ascribed to the ability of binding hydrogen chloride, but also to the replacement of labile chlorine atoms of the PVC chain by stearate groups. In this way the growth of the polyene sequences is inhibited. On the other hand sufficient amounts of pentaerythritol and calcium stearate effectively inhibit the detrimental catalytic action of zinc chloride formed.A mathematical equation was deduced based on this mechanism, which satisfactorily describes the correlations among the induction period, the stabilizer concentration and the ester groups formed during thermal ageing.