Often used to collect dew water during night, radiative cooling is a passive method for cooling enclosed rooms or condensers by radiative exchanges with sky. Recent works aim to develop materials and architectures in order to extend radiative cooling on daytime, in order to refresh buildings, foods or collect water at low energy costs. This paper investigates the properties of materials used to build-up daytime radiative coolers. Nightly energy balance of condensers needs to be modify to account for solar radiation contributions. For cooling purposes, dehumidifying is not the main objective and hence, we are interested in the cooling ratio. A simple architecture, made of encapsulated boxes, is used to model radiative heat fluxes, in visible and infra-red spectrums, with taking into account for direct and diffuse fluxes emitted by the environment. Using a reference scenario for surrounding conditions, the role of wall absorption, emission and reflection is discussed, detailing fluxes on each side of the reflector and cooler boxes. Documented new materials are selected to study radiative surface properties and their effect on the cooling efficiency obtained inside the cold room. Further scenarii are made about thermal conductivities and heat capacities of walls. The global energy balance provides guidelines for designing surface and conductivity matrix to ensure cooling in steady state conditions. The model is used to make a comprehensive estimation regarding various proposals among literature. Few observed temperature decreases are compared with simulation results and cooling efficiencies are analysed: performance indicators are suggested to describe such kind of device, giving an harmonised basis on a daily basis and excluding climatic condition effect. This study provides some technical issues for building daytime condensers, stressing some differences with the nightly operating devices. Further work is needed to compare modelling results with real and fully documented data and discuss about air permeability of boxes to overcome heat storage during most adverse irradiant conditions.