Advances in hydrogel-based materials for improving building energy efficiency

Hydrogels have emerged as highly promising materials for building applications, owing to their tunable physicochemical properties, exceptional hydrophilicity, and robust mechanical strength. Despite significant advances in hydrogel material design, their integration into practical applications and performance improvement in building envelopes and indoor environments remain limited. Herein, we present a comprehensive summary of recent progress in hydrogel-integrated building components with a focus on their roles in smart windows for modulating sunlight dynamically, sorption-based dehumidification systems for effective humidity regulation, and passive thermal management on building surfaces. Hydrogel-based smart windows leveraging thermochromic and electrochromic mechanisms have now achieved up to ∼90 % solar modulation from 20 to 35 °C while maintaining a luminous transmittance of 95 % at 20 °C, and evolved towards multifunctionality. Hygroscopic hydrogels for humidity control and surface cooling have demonstrated a moisture sorption capacity from 0.7 to 2.65 g g⁻¹ at 30 % RH and achieved a temperature drop of 12–25 °C on the rooftop compared to the reference surface without gel covered under 1000 W m⁻² solar radiation for 3 h. Furthermore, we discuss the optimization of heat and mass transfer mechanisms within hydrogels for enhanced sorption and desorption kinetics. Finally, the limitations of current hydrogel materials—including limited interfacial area, poor controllability in parameter regulation, and performance degradation—are highlighted, and perspectives for future composite design are proposed. This review offers in-depth insights, design principles, and optimization strategies for leveraging hydrogels in building envelopes and environments, supporting the transition toward high-performance and low-carbon buildings.