The evolution of the viscosity of two commercial epoxy resin systems subjected to manufacturer's recommended cure cycles was studied in detail. The two systems were characterized through rotational viscosimetry and oscillatory rheometry. It was observed that the different size of the samples in the two setups influenced the kinetics and, thus, the evolution of the cure and viscosity. The differences resided in the effective temperature experienced by the resin at each moment. Original rheological constitutive relations are proposed for each resin system and mass quantity, aiming to capture the real processing conditions. All the experimental and modeling procedures are described in detail and the new rheological constitutive relations are presented. POLYM. ENG. SCI., 54:831-839, 2014. (c) 2013 Society of Plastics Engineers