Fig. 4: Cooling power and outdoor cooling performance measurements of the dual-selective emitter.

a Schematic for the thermal measurement device used to measure the cooling power of samples. b Real-time cooling power measurements of the dual-selective POM-PTFE-Al and mono-selective POM-Al from 11:30 a.m. to 01:30 p.m. (in the Ulan Buh Desert, RH = ~10%, 7 September 2022). The orange region in b indicates the solar irradiation. c, d Infrared test of the dual-selective thermal emitter in an arid outdoor environment (RH = ~10%, 31 January 2023) of Beijing, China (40°0′33″ N, 116°20′0.6″ E). The photograph c and infrared images (d 30 min) of the dual-selective sample and several typical commercial roofing materials, including color steel roof (white, background), uncovered black asphalt (10 × 20 cm²), and covered black asphalt (Al foil-covered, dual-selective film covered, white paint-Al foil covered, and white paint-coated). Scale bar in c = 20 cm. It should be noted that the infrared tests are qualitative, as the colors of an infrared image depend not only on the surface temperature but also on the MIR emittance. The emittance of each sample in the infrared images was not calibrated individually, which is obviously inappropriate for the ultralow emissivity Al foil sample. e Real-time internal temperature measurements (RH = ~10%, Beijing, China, 29 March 2023) of the dual-selective film-covered Al foil box (20 × 15 × 15 cm³) as a proof-of-concept, compared to the uncovered and white paint-coated Al foil boxes (Inset is the photograph of the Al foil boxes for temperature measurement). Source data are provided as a Source Data file.