Partially Oriented Yarn (POY) is a type of polyester filament yarn produced through the molten spinning process, where semi-crystalline polyester chips are melted and extruded to form continuous filaments. This study investigates the relationship between applied load and elongation characteristics of polyester POY manufactured using this technique. The POY samples analyzed were of the semi-dull type and varied in denier and filament count: 114/36, 130/36, and 248/48. Semi-dull polyester chips were processed through an extruder, and the resulting filaments were wound at controlled speeds to produce POY with varying structural parameters. Mechanical testing was conducted to evaluate properties such as load-bearing capacity and elongation behavior. The average elongation values observed were approximately 123.90%, 125.73%, and 138.06% for the 114/36, 130/36, and 248/48 samples, respectively, under corresponding loads of 328.33 g, 348.33 g, and 548.33 g. These results indicate that although elongation tends to increase with applied load, the relationship is not strictly linear. Instead, the data suggest that other influencing factors—such as denier, filament count, and the internal molecular orientation of the yarn—play a significant role in determining elongation performance. Understanding these variables is crucial for optimizing POY properties for downstream processing and final applications in both textile and industrial sectors.