Fused Filament Fabrication (FFF) is a popular additive manufacturing process for creating prototypes and end-use products. Infill patterns, which fill the interior of hollow FFF-printed objects, play a crucial role in determining the mechanical properties and structural integrity of hollow structures. This study investigates the effects of infill line multipliers and different infill patterns (hexagonal, grid, and triangle) on the mechanical properties of 3D printed hollow structures. Thermoplastic poly lactic acid (PLA) was used as the material for 3D-printed components. Infill densities of 25%, 50%, and 75% were chosen, along with a line multiplier of one. The results indicate that the hexagonal infill pattern consistently demonstrated the highest Ultimate Tensile Strength (UTS) of 1.86 MPa across all infill densities, out-performing the other two patterns. To maintain a sample weight below 10 g, a two-line multiplier was utilised for a 25% infill density sample. Remarkably, this combination exhibited a UTS value of 3.57 MPa, which is comparable to samples printed at 50% infill density, which were 3.83 MPa. This research highlights the importance of line multiplier in combination with infill density and infill pattens to ensuring the achievement of the desired mechanical properties in the final product.