## 2 Experimental Section
### Test Method Characterization  
This study was conducted in the temperate monsoon climate of Tianjin, characterized by cold winters and hot summers, focusing on the insulation effects of coatings during winter. The experimental setup included an infrared radiometer (model HL-131, the manufacturer is Shenzhen Lianhuicheng Technology Co., Ltd., Shenzhen, Guangdong, China), a reflective indoor heater (model RSN22-S07), rated at 700 W, 220 V, the manufacturer is Changhong Meiling Technology Co., Ltd., Zhongshan, Guangdong, China), and a thermocouple thermometer (model RE-Y2101B, the manufacturer is Kipsen Technology Industrial Co., Ltd., Guangzhou, Guangdong, China), as detailed in Figure 3b. The thermocouple thermometer recorded the temperatures on both sides of the wall, using indoor reflective heaters as the heat source. The infrared radiometer measured the infrared heat flux, which spans a wavelength range of 0.76-1000 \(\mu\)m.  
Heat flux is defined as the heat received or reflected per unit area of the wall. It is influenced by the wall's thickness, the temperature differential across the wall, and the wall material's thermal conductivity. This metric is crucial for evaluating both the heat dissipation performance and the heat loss of materials. Currently, the evaluation of thermal reflective coatings in buildings primarily focuses on hemispherical emissivity and solar reflectivity. This experiment primarily examined how the wall material, the angle of heat source irradiation, and the duration of irradiation affect the insulation properties of the coatings. The photothermal and thermal reflection performance of the coating were assessed by measuring the temperature difference between the exterior wall and the room temperature, as well as the heat flux reflectance before and after coating application. The test was structured into two primary sections: measuring the temperature and heat flux of three different walls, and monitoring the temperature data in the Earth Survey Building classroom. Prior to applying the coating, temperature sensors were installed at two equidistant points along a diagonal on the rear of each wall segment to ensure accurate  
Figure 3: (**a**) Gouging and embedding temperature sensors. (**b**) Connecting the thermocouple thermometer. (**c**) The temperature sensor is buried on the left view of the wall and the right view of the wall. data collection. These sensors were linked to thermocouple thermometers, as depicted in Figure 3. Initially, the angle (\(\theta\)) between the heat source's central axis and the vertical plane of the wall was set for various measuring points on the three walls, as illustrated in Figure 4a,b. It was necessary to log the temperature of the \"bare wall\" every 30 min, collecting 15 datasets, and of the \"bare wall + heat source\" every 30 s for a duration of 10 min. Subsequently, \(\theta\) was adjusted from 10 degrees to 80 degrees in 10-degree increments to assess the changes in temperature and heat flux. Following this, the temperatures and reflected heat fluxes for the \"wall after a coat of paint\" were recorded every 30 min, with 15 data sets collected, and for the \"wall + heat source after a coat of paint\" every 30 s for 10 min. \(\theta\) was similarly adjusted from 10 degrees to 80 degrees in 10-degree steps, and the measurements continued for three days to evaluate the stability. To capture accurate and reliable data, measurements were taken from four points on each wall, with two points on each side. These points were located at the two-thirds positions along the diagonal of the wall, as shown in Figure 4c. At the start of the experiment, the following were recorded: indoor and outdoor temperatures, indoor and outdoor humidity, radiator temperature, the temperature 60 cm from the radiator, radiator heat flux, and heat flux 60 cm from the radiator. The heat source was consistently positioned 60 cm from the center of the wall.