Radiative cooling presents a promising passive cooling strategy, though its widespread adoption is often constrained by elevated costs and manufacturing complexities. This study introduces a cost-effective, scalable fabrication method for a composite membrane utilizing a spraying technique, and it was fabricated by spraying a mixture of modified nano-zirconia and ethylene-octene copolymer (POE), dissolved in petroleum ether, onto a polyethylene (PE) bubble film substrate. This composite membrane demonstrates a hydrophobic property, with a water contact angle of 100.6°. A cooling structure was formed by covering the composite membrane onto a polytetrafluoroethylene (PTFE) plate which served as an emitter, and the cooling power of this structure reaches 66.2 ± 4.3 W/m². Field tests reveal a temperature reduction of 3 ± 0.3 °C at noon and an average cooling effect of 4.7 ± 0.3 °C throughout the day, relative to ambient temperatures. This work advances the development of cost-effective, scalable radiative cooling technologies, holding promise for applications in building cooling and energy efficiency.