Natural/Synthetic Hybrid Fiber‐Reinforced Polymer Composites: Advances in Interface Engineering, Hybridization Modeling, and Sustainable Manufacturing

Hybrid natural/synthetic fiber‐reinforced polymer composites offer a practical engineering solution by combining the sustainability, low cost, and low density of natural fibers (1.3–1.5 g cm −3 ) with the strength, stiffness, and reliability of synthetic reinforcements like carbon (1.75–1.95 g cm −3 ), glass, or basalt fibers (2.5–2.8 g cm −3 ). This density difference enables strategic, material‐efficient synthetic placement only where structural demands require it. Reported tensile strengths range from 3 to 400 MPa for certain natural fiber systems to 60–784 MPa for specific glass/epoxy systems, highlighting the importance of reporting the fiber fraction, architecture, interface quality, and testing methods in the evaluation. However, weak fiber‐matrix adhesion, fiber variability, thermal instability, moisture sensitivity, and unpredictable multiscale hybrid effects hinder widespread structural use. To address these limits, this review evaluates advancements in composite design, processing, and performance. It focuses on hybrid architectures (interlayer, intralayer, intrayarn); interface engineering (physical, chemical, bio‐based, nanomaterials); predictive tools (analytical, semi‐empirical, data‐driven, digital twins, multiscale FEA); and manufacturing routes (conventional molding, resin transfer, automated fiber placement, additive manufacturing). Crucially, environmental and economic benefits are system‐dependent rather than inherent, requiring a complete accounting of fractions, matrices, treatments, energy, lifespan, and end‐of‐life pathways. By integrating interface design, manufacturing, and performance, this review clarifies the trade‐offs between sustainability and reliability, thereby establishing priorities for engineering scalable, lightweight, and durable hybrid composites.