Fused deposition modelling (FDM) is the popular but complex additive manufacturing process that works with many process parameters, which are crucial to investigate. In this study, 3D parts are fabricated by placing each filament layer in opposite direction to each other, for that two combinations of raster angles [45° -45°] and [0° 90°] along with three different infill speeds are used. In this study the two 3D printing material types - Polylactic Acid (PLA) and tough-PLA are used. The material properties of each 3D part are investigated to identify the best combination of these parameters. The microstructural analysis is also performed on outer and inner surfaces along with fracture interface of the parts after tensile testing using a scan-ning-electron-microscopy (SEM) to explain material failure modes and reasons. The results sug-gest that, for both the material types, the raster angle [45° -45°] produces the strongest parts compared to the raster angle [0° 90°]. This study also suggests that slow infill speed gives improve tensile properties by providing better inner-connection between two contiguous roasters. Thus, detailed analysis of microstructural defects correlated with tensile test results provided an insight on the optimisation of raster angle and infill speed, and scope for improvement of mechanical properties