Polyester (PET) materials have become more common as reinforcement solution in reinforced soil walls (RSW). It has been shown that strength and stiffness of geosynthetics products, including PET, is load-, time-, and temperature-dependent. Consequently, the mechanical response of these materials is influenced by in-soil conditions. The present study describes viscoelastic and visco-plastic constitutive formulations used to model PET strap reinforcement layers in thermo-mechanical finite element models. The models are demonstrated using an idealized 15-meter high RSW with concrete facing panels, including loading due to a road at the top of the structure. Reinforcement model parameters were calibrated using laboratory measured data. Analyses include temperature boundary conditions representing a Mediterranean climate for a 1-year period following end of construction. Calculated stress and strain values were in accordance with values found in the literature. The results of this study are a precursor for the long-term modelling of RSWs under operational conditions subjected to changing atmospheric boundary conditions.The authors wish to thank Aaron Kim from GECO Industrial (Korea, Rep.) for providing polymeric strap data from manufacturing quality control records. The authors wish to acknowledge the support of the Department of Civil and Environmental Engineering (DECA) of the Universitat Politécnica de Catalunya�����BarcelonaTech (UPC) and the International Centre for Numerical Methods in Engineering (CIMNE) and the funding received from the Spanish Ministry of Economy and Competitiveness through the “Severo Ochoa Programme for Centres of Excellence in R&D” (CEX2018-000797-S-20-4).Peer ReviewedPostprint (published version