<p>This study investigates a novel treatment involving the incorporation of silver nanoparticles (AgNPs) onto vegetable fibers, assessing its impact on dimensional stability and fiber–matrix interaction for potential application in cementitious composites. The treated fibers underwent comprehensive analysis of their physical, thermal, morphological, and mechanical properties. The AgNP impregnation method demonstrated its capacity to modify fiber surfaces, leading to increased roughness, improved dimensional stability, and reduced water absorption. These observed enhancements are attributed to the combined effects of thermal cycling and the low pH of the AgNP solution, which likely induced alterations in the fiber microstructure. Mechanically, the treated fibers did not exhibit statistically significant differences in tensile strength or Young’s modulus. While AgNP impregnation did not yield statistically significant changes in fiber–matrix adhesion, a notable qualitative shift in the typical curve behavior, from softening to hardening, was observed. These findings suggest that AgNP treatment of vegetable fibers holds promise for influencing properties relevant to cementitious composites, warranting further investigation into its long-term efficacy and specific applications.</p>