Application of Infrared-Blocking Agents for Optical Clarity, Thermal Control, and Long-Term Durability Abstract Architectural window films are designed to reduce solar heat gain while maintaining natural daylight, visual transparency, and indoor comfort. In practical formulation and coating development, however, improving infrared-blocking performance may also lead to reduced visible light transmittance, increased haze, color deviation, coating temperature rise, dispersion instability, and reduced outdoor durability. The application of an infrared-blocking agent should therefore not be evaluated solely by the infrared rejection measured at a single wavelength. Product development should consider the complete solar spectrum, nanoparticle dispersion, resin compatibility, coating thickness, glazing configuration,