LAUSR

3D printing technology has transformed the production of complex sandwich composite structures and offers exceptional control over material selection. PLA‐based composites are favored for load‐bearing applications due to their renewability and durable mechanical properties. However, their interaction with water poses a major challenge as moisture can severely affect their performance. This study investigates the effects of water absorption on the mechanical properties, energy absorption, and failure modes of 3D‐printed sandwich composite structures made of PLA‐based materials (PLA, PLA–Carbon, and PLA–Wood) under quasi‐static loads such as flatwise, in‐plane, and flexural tests. The results show that PLA–Wood has the highest water absorption among the composites due to its hydrophilicity, resulting in a significant reduction in compressive strength and Young's modulus by 19 and 9%, respectively, in flatwise tests, due to severe degradation. In contrast, PLA–Carbon shows superior energy absorption with values of 277.91, 10.74, and 1.73 J in flatwise, in‐plane and flexural tests, respectively, compared to 163.83, 2.47, and 1.17 J for PLA–Wood. This difference results from the ability of PLA–Carbon to deform in a controlled deformation, whereas PLA–Wood is susceptible to severe structural deformation. These results emphasize the durability of PLA‐based composites for load‐bearing applications, especially in moisture‐prone environments.