This study presents an investigation of theAmazônica fibers performancePolymer composites of polyester matrix polymer compositesPolymer composites reinforced with short fibers of envira cheirosa (Annona paludosa Aubl.), an AmazonianAmazonian fibers species still little explored in engineering. The research involved physical characterizationsCharacterization, flammability tests, and mechanical tensile tests, complemented by fractographic analyses using scanning electron microscopy (SEM). In this context, the aim was to understand the influence of short fiber addition on the structural, thermal, and mechanical propertiesMechanical properties of the compositeComposites. The results indicated that fiber incorporation increased porosity and water absorption, altered the burning behavior, and provided limited mechanical improvements, mainly at intermediate reinforcement concentrations. Microstructural analysis revealed interfacial adhesion failures, the presence of voids, and pull-out mechanisms, factors that explain the limitations of the observed mechanical propertiesMechanical properties. Thus, although envira cheirosa shows potential as reinforcement, the compositeComposites’s efficiency directly depends on the quality of the fiber–matrix interface. Therefore, this study contributes to advancing knowledge on the application of Amazonian natural fibersNatural fibers in polymerPolymer materials, broadening perspectives for their sustainable use.