Specimens of high impact polystyrene and polyurethane were studied for creep at room temperature and constant tensile force without aging and after aging according to various programs. For polyurethane specimens after aging, an increase in creep time for a given deformation by 3 times compared to specimens without aging is observed. For high impact polystyrene in the creep experiments after aging, a decrease of deformation by 6.5 times and the time to fracture by more than 24 times, compared with specimens without aging is shown. To describe the obtained experimental creep curves for polyurethane and polystyrene specimens without aging and after aging, modified versions of linear elastic-viscous models of Maxwell and Voigt written in the effective time scale are used. A good agreement between the theoretical and experimental creep curves is observed.