A Comprehensive Review of High‐Solids Waterborne Polyurethane: Design Strategies, Performance Enhancement, and Future Perspectives

ABSTRACT High solids content waterborne polyurethane (HSWPU) has emerged as a key environmentally friendly material for coatings, adhesives, and elastomers due to its non‐toxic nature, low VOC emissions, and excellent performance. This review provides a comprehensive overview of HSWPU, systematically analyzing the design strategies, performance enhancement methods, and underlying mechanisms that govern solids content and viscosity. The discussion is structured around three core aspects: (1) the role of hydrophilic monomers (anionic, cationic, non‐ionic) and their synergistic effects; (2) the influence of microstructure, including particle size distribution, crosslinking density, hydration layer thickness, and particle deformability; and (3) the impact of polyol selection, with a focus on sustainable bio‐based alternatives such as vegetable oils. Key theoretical frameworks—including electric double layer theory, multimodal particle size distribution, and hydration layer theory—are integrated to elucidate their synergistic interplay in determining emulsion stability and rheology. Furthermore, the review summarizes quantitative performance comparisons of various modification strategies, provides recommended particle size ranges for different coating functions, and explores emerging applications in flexible electronics and corrosion‐resistant coatings. Finally, future research directions are outlined, emphasizing sustainable material sourcing, multifunctional integration, and the need for standardized characterization protocols.