Hygrothermally decomposed polyurethane (HD-PUR) was mixed up to 20 phr in epoxidized natural rubber (with 50 mol % epoxidation; ENR50) recipes, and the curing and mechanical behaviors were studied. Mechanical testing of the ENR50/HDPUR vulcanizates determined the tensile, tear, compression-set, hardness, abrasion, hysteresis, and resilience properties. No significant changes were observed in the tensile properties with the incorporation of HD-PLTR. The ENR50 compounds showed an increase in compression set with increasing HD-PLTR content. Rubbers cured by a semi-efficient vulcanization system gave the best overall performance. A further improvement in curing and mechanical properties was achieved by the carbon black grade N330 being replaced with a more active grade (N375).