The marketplace has shifted for over decades towards biobased polyols manufactured from renewable feedstock to improve the industry's sustainability. As a result, the desire for biobased polyols has risen fast, creating the significant potential to convert biomass into polyurethane polyols. Bio-based polyol from expired sunflower oil was utilized as a partial substituent to the commercial polyol for making rigid polyurethane foam. Polyester polyol was synthesized via trans-esterification of glycerol followed by polycondensation with phthalic anhydride. The mechanical properties of the resulting foam were performed to identify the impact of this replacement. The SEM image shows deterioration in the foam cells in the substitution of over 30%. The 50 percent bio-based substitute, on the other hand, causes the cells to deteriorate. Foam density increases due to the long chain of the bio-based polyol. The greater density of the bio-based polyol than the commercial polyol is responsible for the increased foam density. The compressive strength values increase with the rise of the bio-based content. This increase was attributed to the increase in polyurethane flexibility. The minimum thermal conductivity was obtained in the 30% bio-based polyol substitution. At this value, the foam shows regular foam compared to higher substitution ratios. The results present a sustainable and eco-friendly source for polyurethane production.