The composite materials are present in nature since the prehistoric era. Applications of fiber-based composite materials are increasing day by day in our society to overcome the raised environmental and economic concerns. Hence, waste fiber can be utilized as the best resource to develop composites.

The present study deals with the impact of hybridization on the mechanical, thermal, and water absorption behavior of hair and coir fiber-based hybrid composites. The compression molding technique was used to develop the hybrid composites with fixed fiber content (15 wt.%) and was also varied the relative weight percentage of hair and coir fibers [(100% HF), (75% HF/25% CF), (50% HF/50% CF), (25% HF/75% CF) and (100% CF)] in reinforcing phase with HDPE composites S₁, S₂, S₃, S₄, and S₅, respectively. The composite S₂ was achieved superior mechanical attributes as compared to other hybrid/non-hybrid composites. The composite S₂ was improved the tensile strength 5% and 35.2% more in comparison to composites S₁ and S₅, respectively. The thermal behavior (TGA, DTG, and DTA) was also influenced by the blending ratio of fibers of composites. The 5% and 50% weight losses of composite S₂ were observed at higher temperature 343.8°C and 465.8°C as compare to other composites, which showed the thermal stability of composites S₂. SEM analysis was used to investigate the strength of the fiber-matrix interface, which was shown a significant connection between mechanical and thermal behaviors. The crystallinity of hybrid and non-hybrid composites was examined by using the X-ray diffraction (XRD) analyzer and composite S₂ was achieved 326 × 10⁻⁹ m crystal size at 21.053° peak position with wavelength 1.5406 × 10⁻¹⁰ m for Cu. The water absorption test was used to examine the moisture resistivity of composite materials, which was helpful to increase the applications of materials in humid areas.