Day‐Night Passive Thermoregulators via Dynamic Spectral Modulation

Abstract Passive thermoregulators enabling zero‐energy temperature regulation hold immense potential for sustainable thermal management. While existing thermoregulators struggle with conflicting daytime reflectivity modulation and nighttime insulation requirements, a dynamic spectral modulation thermoregulator through the synergistic integration of low‐emissivity films, thermochromic components, and specular reflectors is proposed. The thermoregulator achieves high visible reflectivity modulation (ΔR = 0.29–0.42 for red, blue, green, and black), high near‐infrared reflectivity (0.90), and low mid‐infrared emissivity (0.05). Field tests revealed that the visible reflectivity modulation drives a daytime temperature reduction of 5.1 and 1.5 °C compared to black low‐ and high‐emissivity references, respectively. Furthermore, the nighttime thermal insulation sustains a 2.4 °C thermal warmer than conventional high‐emissivity devices. When stabilizing room temperature at 28 °C, the thermoregulator achieves cooling power savings of 37.34 and 40.50 against low‐ and high‐emissivity references, respectively. The easily fabricated thermoregulator offers a promising solution for passive temperature control and energy saving.