This study aims to investigate the mechanical properties, absorption properties, morphology, and thermal properties of eggshell filler material combined with water hyacinth (WH) plant ash composites. This research aims to develop eco-friendly particle board and medium-density board products using WH plant ash particles for commercial applications. There is only a small amount of previous literature on ash particles with eggshell filler material derived from aquatic wastes of hyacinth plants combined with polymer composites. Eggshell powder is used in this study as a filler. This filler enhances the mechanical properties of hyacinth ash composites. As a result of the drying process and the open-air burning, ash particles are produced from the hyacinth plant. Mechanical (tensile, flexural, and impact) and absorption tests are conducted according to ASTM standards. In order to measure chemical and essential functions, X-ray diffraction and Fourier transform infrared techniques are used. By using a scanning electron microscope, it can be determined how ash particles bond, how eggshell powder combinations work, and how primary (ash particle) and secondary phase (epoxy) materials are absorbed. Based on the final experimental results, it appears that the composite hyacinth ash particle samples made with eggshell filler are highly recommended for particle board and medium-density board because of their mechanical strength and hardness.