This study evaluated its impact on thermal, mechanical, and hydrophobic properties, analyzing its feasibility in precast elements. Specimens with fiber substitutions between 2.50% and 17.50% were produced, and their thermal (thermal conductivity), mechanical (bulk density, flexural strength), and hydrophobic (water vapor permeability) properties were analyzed. The results indicated that the incorporation of fiber reduced the density and thermal conductivity by 9.71% and 56.33%, respectively, and improved the resistance to the passage of water vapor by 11.11%. These improvements suggest that coconut fiber contributes to optimizing the performance of the material, favoring its application in prefabricated panels. From a broader perspective, these findings support the use of agricultural by-products in construction, promoting the circular economy and contributing to the reduction of CO₂ emissions in the sector.