Radiative sky cooling utilizes the high transmittance in the “atmospheric window” (8–13 μm) to effectively dissipate heat as thermal radiation to the cold outer space. This study investigates the cooling performance of radiative cooling materials applied to three different building materials: cement, metal, and fribic. Spectroscopic testing indicated that the average emissivities of radiative cooling coatings were 0.95 in the “atmospheric window” (8–13 μm) band. In the AM 1.5 solar spectrum (0.25–3.0 μm) band, the average reflectivity of the radiative cooling coatings on metal substrate was higher to be 0.578. In comparison, the average reflectivity of the radiative cooling coatings coated on cement was relatively lower to be 0.509. Outdoor experiments were conducted and the results revealed that during the daytime, the peak surface temperature of the radiative cooling coating on the cement substrate was recorded at 1.2 ℃ below the ambient temperature, demonstrating effective cooling capabilities. Meanwhile, the radiative cooling coating applied to the fabric substrate exhibited the highest surface temperature, at 8.1 ℃ above the ambient temperature. At night, the surface temperatures of the radiative cooling coatings applied to the three building material substrates ranged from 8.0 °C to 8.6 °C below the ambient temperature. The results indicated that the different substrate materials influence the radiative cooling performance, especially in the daytime. Such difference should be taken into consideration in practical applications.