This study investigates the theoretical modeling and experimental analysis of composites made from randomly oriented flax fibers reinforced with recycled expanded polystyrene (EPS) waste. The effect of flax fiber volume fractions (20%, 30%, and 40%) on the composites' tensile strength and tensile modulus were examined. Several theoretical models namely the rule of mixtures (ROM) series, modified Bader and Bowyer, Hirsch, Cox-Krenchel, and Einstein-Guth model were compared against the experimental results of the formulated composites. The theoretical predictions of tensile strength from the Hirsch and modified Bader and Bowyer models showed close alignment with experimental results. Cox-Krenchel and Hirsch's models better predict the tensile modulus of a composite at 30% fiber loading. Additionally, this research accentuates the potential of utilizing natural fibers in combination with recycled EPS materials to produce eco-friendly composites with better performance for construction applications, such as house panels and automobile interior components.