A reaction system for forming polyurethane elastomers includes a cardanol modified epoxy polyol. In particular, the reaction system has an isocyanate-reactive component that includes the cardanol-modified epoxy polyol and an isocyanate component that includes at least one polyisocyanate. The cardanol-modified epoxy polyol is a reaction product of an epoxy component and an epoxy-reactive component at a ratio of epoxy groups to epoxy reactive groups from 1:1 to 1:5, and the epoxy-reactive component includes a cashew nutshell liquid having a cardanol content of at least 85 wt %, based on a total weight of the cashew nutshell liquid.