This paper discusses the properties of interconnected interpenetrating polymer networks (IPNs) based on polyurethane (PU) and polystyrene (PS), formed by varying the PU/PS ratio. The interconnected IPNs were prepared by first forming a PU network based on an unsaturated polyester polyol with toluene diisocyanate in the presence of a triol, followed by interconnecting the PU chain segments by reaction of styrene with sites of unsaturation. Five such IPNs have been prepared at PU/PS ratios of 100/0, 90/10,80/20, 70/30, and 50/50. The properties of these IPNs have been rationalized on the basis of the structure of these IPNs reported in an earlier communication. The mechanical properties, namely, tensile strength at break and elongation at break, have been shown to correlate well with the cross-link factor (CLF) of the IPNs. CLF is a measure of the number of cross-link points per gram of the resin. The tensile recovery behavior has been explained on the basis of the morphology of the IPNs. The dynamic mechanical analysis of the interconnected IPNs having a PS content up to 30% have shown only one glass transition temperature (T(g)) corresponding to the PU phase. The T(g) of the PS phase was not observed in the temperature range employed. In the case of IPN containing 50/50 PU/PS, two T(g)’s were observed corresponding to PU and PS phases due to the coiled configuration of the PS bridges. The dependence of the Molecular weight between cross-links (M(c)) of the IPNs on the PS concentration showed a trend similar to that of the CLF. The permeability studies showed that the flux of N2 and CO2 gases through the IPNs is governed by the cross-link density and the morphology of the IPNs. The thermal degradation behavior of the IPNs was rationalized on the basis of the structure.