This paper explores a hybrid- and two mono-nanofluids and, to be more specific, it deals with the effect of adding Silica (SiO2) and Graphene (G) nanoparticles and their hybrid (G (30%) + SiO2 (70%)) on viscosity of water. For all designed hybrid- and mono-nanofluids at various concentrations of 0.05–1%, viscosity was measured under the influence of temperature (25–50 °C). (320 characters)