Developments by Labuschagne et al. (2006) in the manufacture of Layered Double Hydroxides (LDHs) have led to a patent describing a new effluent free synthesis method. To make the LDHs produced using the new synthesis method commercially viable requires that they have product applications. One such application is as a thermal stabiliser and fire retardant for poly(vinyl chloride) (PVC). The problem is that a PVC compound is a complex system that includes multiple additives that tend to interact strongly with each other. The aim of the investigation was to quantify and analyse the effect of an LDH on the important material properties of a flexible PVC compound. The effect of a Hydrotalcite-like LDH on the thermal stability, fire retardancy and basic mechanical properties was modelled using 2nd degree Scheffe polynomials. The empirical models for each response variable were determined using statistical experimental design. The particular models for each response variable, which are selected for predictive ability using k-fold cross validation, were interpreted using statistical analysis of the model terms. The analysis clearly shows and quantifies the significant effect that the LDH has on increasing the long term dynamic thermal stability and decreasing the smoke production of the PVC compound. The positive effects that the LDH has are offset by the negative effect it has on the elongation at break of the PVC compound. The analysis also reveals a number of interactions between the LDH and other additives. For instance, a strong synergistic relationship between the LDH and the plasticiser in terms of thermal stability and smoke reduction is evident, which to the knowledge of the authors has not been reported in the literature. There is also, somewhat surprisingly, evidence of antagonism between the LDH and the primary thermal stabiliser with regard to the thermal stability of the PVC compound.