Synthetic fiber-based polymeric matrix composites have a significant environmental effect throughout their manufacture, disposal, and recycling processes; in response, eco-friendly composites made from materials derived from natural resources have been created. The disposal of agro-waste from industrial crops has emerged as a pressing issue in low-income regions in recent years. The availability of agro-wastes means that it may be used to create sustainable composite materials, which is a promising trend for the building sector. However, it has been demonstrated that the natural fibers’ propensity to absorb water is the single most important contributor to the irreversible degradation of the resulting composites’ qualities over time. This chapter aims to report research on the water absorption characteristics of agricultural fiber-reinforced polymer composites as thoroughly as possible. Since petroleum-based goods contain nonbiodegradable polymers, which break down over time and produce hazardous chemicals and gases, their ongoing distribution of E-waste poses ecological and environmental challenges. This leads to the development of biodegradable polymers and fibers, which are biocompatible and naturally biodegrade in their surrounding habitats, relieving environmental stress in the process. Flexibility, dielectric characteristics, electrical properties, and water and gas vapor barrier qualities are all areas in which biobased materials fall short. Current studies are geared at developing methods of improving the characteristics of biodegradable composites by including a variety of nanostructures. The environmental benefits of using biopolymers and biofibers as raw materials are a primary motivation for their widespread adoption. To improve the properties of biopolymer-based composites, scientists now frequently add nanofillers to the mix. To keep the nanocomposite materials at their optimal density and to improve their mechanical, thermal, flame retardant, and water absorption characteristics, nanofillers will be used as additives. Due to their increased surface area, aspect ratio, and improved characteristics, nanocomposites have found increased use in a wide variety of industries. Research into the production of biodegradable agricultural mulch films has been bolstered by the present necessity to eliminate the buildup of synthetic polymer waste during the growing and harvest of food. An alternative is provided in the form of native and oxidized thermoplastic maize starch, with and without the inclusion of natural and modified bentonite (Bent) with an eco-friendly natural polymer such as chitosan (CS). This chapter looks at how absorbing water affects the mechanical characteristics of composites. This chapter covers the different functional features of nanocomposites and their applications and describes the different types of biofibers/biopolymers.