This study investigates the synthesis, stability, thermophysical properties, and figure of merit (FOM) analysis of Cu-graphene hybrid nanofluids as a potential alternative to conventional heat transfer fluids. The hybrid nanofluids were synthesized by dispersing Cu and graphene nanostructures in water at very low concentrations (0.04 vol % Cu and 0.01–0.1 vol % graphene). The hybrid nanofluids exhibited excellent stability against aggregation for up to 7 weeks, as evidenced by high zeta potential values. Thermophysical properties such as thermal conductivity, viscosity, and specific heat were measured and found to significantly improve with increasing hybrid nanostructure concentration. The thermal conductivity of the hybrid nanofluids showed an exceptional enhancement of ~35% at low concentrations, while viscosity increased substantially compared to water. The FOM analysis revealed that the Cu-graphene hybrid nanofluids are suitable for use in laminar flow conditions, as their FOM value exceeds 1, indicating better thermal performance than conventional fluids. However, they are not effective under turbulent flow conditions due to their lower FOM value. The study also validated the thermophysical properties of the hybrid nanofluids using existing theoretical models. The results demonstrate that Cu-graphene hybrid nanofluids offer improved thermal performance and stability, making them a promising candidate for various heat transfer applications.This study investigates the synthesis, stability, thermophysical properties, and figure of merit (FOM) analysis of Cu-graphene hybrid nanofluids as a potential alternative to conventional heat transfer fluids. The hybrid nanofluids were synthesized by dispersing Cu and graphene nanostructures in water at very low concentrations (0.04 vol % Cu and 0.01–0.1 vol % graphene). The hybrid nanofluids exhibited excellent stability against aggregation for up to 7 weeks, as evidenced by high zeta potential values. Thermophysical properties such as thermal conductivity, viscosity, and specific heat were measured and found to significantly improve with increasing hybrid nanostructure concentration. The thermal conductivity of the hybrid nanofluids showed an exceptional enhancement of ~35% at low concentrations, while viscosity increased substantially compared to water. The FOM analysis revealed that the Cu-graphene hybrid nanofluids are suitable for use in laminar flow conditions, as their FOM value exceeds 1, indicating better thermal performance than conventional fluids. However, they are not effective under turbulent flow conditions due to their lower FOM value. The study also validated the thermophysical properties of the hybrid nanofluids using existing theoretical models. The results demonstrate that Cu-graphene hybrid nanofluids offer improved thermal performance and stability, making them a promising candidate for various heat transfer applications.