<p>In recent years, thermochromic smart windows have played an important role in enhancing energy efficiency and contributing to carbon neutrality in building energy consumption. However, thermal-shielding smart windows with high visible light modulation and structural colors are rarely reported. This study focuses on the development of thermochromic smart windows utilizing poly (<i>N</i>-isopropylacrylamide) (PNIPAm)-based nanogels, which exhibit dynamic solar modulation and high visible light transmission without additional energy input. Unlike traditional electrochromic materials such as tungsten trioxide, these smart windows achieve structural color states through the self-assembly of nanogels, eliminating the need for inorganic materials. The fabricated hydrogel contains thermo-responsive poly(<i>N</i>-isopropylacrylamide-random-acrylic acid-random-<i>N-tert</i>-butyl acrylamide) P(NIPAm-r-AA-r-TBA) (PNTA) nanogels with tunable phase transition temperatures (<i>T</i>_p) that align with ambient conditions. These smart windows demonstrate excellent stability over 100 heating-cooling cycles and significant temperature regulation, achieving an indoor temperature modulation of 10 °C and energy savings of 14.24 KJ m⁻³ compared with normal windows. The production process is simple and scalable, making it feasible for industrial applications. Furthermore, these smart windows offer additional functionalities such as information encryption, adding value to their practical application.</p>