Waste generation rates are increasing so there is a need to determine alternative methods of dealing with waste to accommodate a sustainable future. Polyethylene Terephthalate (PET) plastic represents a large portion of the domestic waste generated. This research focuses on characterizing the mechanical and physical properties of recycled PET bales and their constituents after being processed at a material recovery facility. The intent of this study was to assess the technical feasibility of using recycled PET bales as lightweight fill in embankments and engineered slopes. The tensile strength and short-term, one-dimensional deformation characteristics of recycled PET bale constituents were evaluated using full-bottle and chopped PET plastic test specimens. The long-term deformation (creep) of a full-scale PET bale was tested during a large scale unconfined compression test. Additionally, the shear strength of the PET bale constituents were evaluated using a modified direct shear apparatus and triaxial compression tests. A detailed description of the materials tested, the testing protocol developed for each test, and the results and analysis for each evaluation will be presented in this dissertation. The results from all tests conducted herein were subsequently utilized in limit equilibrium analyses to assess the feasibility of using recycled PET bales as lightweight fill in slope stability applications. The analyses systematically evaluated multiple lightweight fill configurations within two slope inclinations and two different soil conditions. The recycled PET bales were compared to EPS Geofoam and tire bales.