Two types of linear low-density polyethylenes, prepared by metallocene catalysts were studied experimentally in terms of differential scanning calorimetry, dynamic mechanical analysis (DMA), and tensile testing. The different comonomer content and the small amounts of long branching in one of the materials studied strongly affect the crystalline distribution and morphology and, consequently, the DMA and tensile experimental data. From the experimental DMA data, the function of relaxation modulus, treated as a material property, is used to describe the corresponding tensile experimental results. A constitutive analysis that considers the viscoelastic path at small strains and the viscoplastic one at high strains proved to be capable of describing the tensile behavior of the materials. (C) 2003 Wiley Periodicals, Inc.