Bio‐Based Polyurethanes: Mechanical Performance, Structure–Property Relationships, and Future Directions

ABSTRACT Driven by growing environmental concerns and increasing regulatory pressures, bio‐based polyurethanes (Bio‐PUs) derived from renewable resources such as vegetable oils and lignocellulosic biomass are attracting significant interest as sustainable alternatives. This review critically examines their mechanical performance, with a particular emphasis on fundamental structure–property relationships. The inherent chemistry of bio‐derived polyols and isocyanates, including hydroxyl functionality, molecular weight, and aromatic or aliphatic nature, is a key determinant of tensile strength, elongation, modulus, and toughness. We highlight effective reinforcement strategies utilizing natural fibers, nanomaterials, and hybrid fillers to enhance stiffness, strength, and thermal stability without compromising sustainability. A comparative analysis with petrochemical PUs reveals that certain bio‐based formulations can achieve comparable elasticity, and toughness, and in some cases improved weathering resistance depending on the specific bio‐derived components and formulation strategies. However, challenges remain in consistently achieving the high rigidity, flame resistance, and long‐term durability typical of some petrochemical PU systems. Broader life‐cycle considerations are also discussed, including feedstock variability, cost competitiveness, and end‐of‐life management. Finally, emerging pathways such as non‐isocyanate polyurethanes (NIPUs), advanced nanocomposites, and digital manufacturing techniques are highlighted as promising strategies to address current limitations and expand the potential application scope of Bio‐PUs, including in structural and biomedical fields.