may cause power blackouts. [1] Moreover, the refrigerant gases used in air conditioners are one of the largest contributors to greenhouse gas emissions. [2] Passive cooling, e.g., cooling with no power input and without greenhouse gas emission, provides an attractive solution to alleviate the power demands as well as negative environmental impact of building cooling. Recent theoretical and experimental demonstrations of subambient daytime radiative cooling (SDRC) represent a breakthrough in realizing passive daytime cooling. [3-21] These radiative cooling materials exploit the infrared transparency window of the atmosphere, in the wavelength range of 8-13 µm, to directly transmit heat from an object at ambient temperature, through blackbody radiation, to the cold outer space which has a temperature of 3 K (−270 °C). This radiation effect, in fact, is what causes one to feel chilly when staying outside in summer nights. However, to generate subambient daytime cooling under direct sunlight using the same effect, the materials must overcome the heating generated by the direct sunshine. In

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The capillary absorption test is one of the most frequently performed material characterization tests. It provides the capillary absorption coefficient and the capillary moisture content, both are important material properties. Currently, full consensus concerning the experimental protocol and data processing of the capillary absorption test has not been reached yet. This paper studies the potential impact factors during the test and compares different methods for processing the raw data. Measurements on calcium silicate, ceramic brick, sintered glass and autoclaved aerated concrete are carried out, and published literature results are reviewed. The impact of sample size, sealing method, initial moisture content, temperature and personnel have been thoroughly analyzed, and proper recommendations are provided accordingly. Moreover, a new data processing model with a solid physical background for calculating the capillary absorption coefficient and the capillary moisture content has been proposed. It shows obvious advantages over other published models and is applicable for both ideal and irregular capillary absorption patterns.