The applicability of a functional polynomial of third degree for the constitutive equation of a nonlinear viscoelastic polymer has been investigated. A method for the determination of the kernel functions appearing in the one‐dimensional creep formulation has been discussed. Creep measurements of tension and compression in low density polyethylene under single step, two step, and three step loading histories are described. The analysis of this data has provided a basis for determination of the creep kernel functions. For the loading range used in the test, the Volterra‐Fréchet multiple integral expansion of the constitutive functional of low density polyethylene has been found to be adequately represented by the three‐term integral representation. A number of cases of general load histories was investigated. A close comparison between the experimental response to these loading histories and the response predicted by the three‐term integral representation was obtained.