The emergence of Fused Filament Fabrication (FFF) technology has opened new avenues for researchers to create intricate geometric structures, particularly for designing high-impact energy-absorbing structures across various applications. This study focused on conducting impact tests to quantify the energy absorption capabilities of two types of fused filament-fabricated polymer composites: carbon fibre-reinforced poly-lactic acid and graphene-reinforced poly-lactic acid. The investigation involved varying infill patterns and infill densities. Among the various infill patterns and densities tested, it was found that a concentric infill pattern with a 90% infill density demonstrated the highest energy absorption performance for carbon fibre-reinforced poly-lactic acid. The experimental data from the impact tests clearly indicated that the impact strength was directly correlated with both infill density and infill pattern. Specifically, adjusting the infill density resulted in a reduction in the impact strength of the printed specimens. To gain further insights into how the energy-absorbing behaviour depended on the chosen process parameters, an analysis of variance using Taguchi’s method was applied to the impact test results. Additionally, the examination of fractured surfaces using scanning electron microscopy (SEM) revealed various types of voids and showed improved interlayer adhesion for different composite materials. This research significantly contributes to our understanding of the mechanical properties of PLA (poly-lactic acid) and its composites. The knowledge gained from this study has the potential to drive advancements in the fields of material science and FFF technology, with broader implications for applications requiring high-impact energy absorption.