Phase‐Change Microcapsules Enable Polyoxymethylene‐Fiber‐Based Aerogels With Enhanced Sub‐Ambient Radiative Cooling and All‐Day Thermal Management

Current radiative cooling materials face significant challenges in managing temperature fluctuations between day and night. Although phase change materials can provide a thermal management effect through reversible phase transitions, their high thermal conductivity leads to a fast thermal response, which hinders efficient radiative cooling and thermal insulation. In this work, a bilayer aerogel composite is developed by integrating a polyoxymethylene‐fiber‑based aerogel outer layer with a sodium alginate‐based aerogel inner layer with phase‐change microcapsules incorporated, thereby enhancing radiative cooling while providing thermal insulation and buffering. With such an integrated design, an average solar reflectivity of 93.53% over 0.3–2.5 µm and a high average emissivity of 96.11% within the atmospheric window (8–13 µm) are achieved in the outer layer, while a high latent heat capacity of 159.8 J g −1 and a low thermal conductivity of 0.0678 W m −1 K −1 are maintained in the inner layer. Owing to these characteristics, the bilayer aerogel composite exhibits maximum temperature differences of −18.3°C (daytime) and +9.3°C (nighttime) between the sub‑ambient and internal cavity ambient temperatures. These values are 8.0°C lower and 4.4°C higher than those of the bilayer aerogel composite without phase‐change microcapsules, respectively. Thus, the developed composite shows potential for sustainable and environmentally friendly thermal regulation in buildings.