Recent research has shown that it is possible to achieve significant cooling by radiative methods without the use of mechanical equipment that require significant amount of electrical power. These passive cooling methods rely on reflecting most of the solar radiation and emitting radiation in the “atmospheric window” wavelength ranges where the atmosphere is transparent, so that a surface exchanges radiation directly with the extremely cold outer space. This literature review noted that almost all published experimental studies on radiative cooling were conducted under different environmental conditions and methodologies, making it almost impossible to compare the results. In this paper, we present a literature review, focusing on daytime radiative cooling performance, that showed an array of testing methods and environmental conditions, leading to the research question of how these technologies would compare with the same testing standard. Slight variations in environmental conditions, setup, and instrumentation from one experiment to another can present large differences in reported performance, even for the same passive radiative cooling device. Examples of setups include non-standard insulated testing chambers, convection barriers, vacuum chambers, shading devices, and instruments like feedback heaters, pyranometers, infrared radiometers and thermocouples. The testing methods reviewed point to the need for a standard cooling potential performance measurement method for the advancement of passive radiative cooling technology.