A reaction system, such as for forming a rigid polyurethane foam, includes a flame retardant polyol that is a brominated reaction product of a cardanol component, a bromine component, and an additive component. The cardanol component includes at least 80 wt % of cardanol, based on the total weight of the cardanol component, and the bromine component including at least 80 wt % of bromine, based on the total weight of the bromine component.