The development and improvement of passive daytime radiative cooling materials (PDRC) have gained significant attention in recent years due to their ability to provide cooling without energy consumption. Climate change and rising temperatures are expected to increase the demand for electricity generation capacity, potentially leading to a “cold crunch”. Passive cooling materials can significantly reduce the energy demand of buildings and cooling systems, as well as industrial cooling processes, by reflecting solar radiation and emitting thermal energy into space through the transparent atmospheric window, achieving sub-ambient temperatures. The evaluation of their cooling capabilities is therefore crucial. This study presents an experimental setup enabling the measurement of the cooling power of four different passive radiative cooling materials under identical boundary conditions. The experimental setup was developed during the European Union funded 21GRD03 PaRaMetriC project. The design, supported by numerical simulation, is based on a liquid-filled temperature control plate that can be adjusted within a temperature range of 10–30 °C, allowing the testing of the PDRC materials at different temperatures. The cooling capacity is determined through the measurement of heat flux and temperature variations. The experimental setup includes a weather station to record and analyse the influence of environmental parameters such as humidity, cloud coverage, and ambient conditions on the performance of the materials. The robust design allows long-term measurements even in challenging weather conditions like rain and storms. It provides a systematic and precise methodology for evaluating PDRC materials.