Abstract: To investigate the effect of liquid-wetting on their microstructure and determine their structural stability to capillary tension, nano-porous thermal insulating materials were directly immersed in absolute alcohol or deionized water, and then they were dried under room temperature and atmospheric pressure. The microstructure of the materials was characterized by nitrogen adsorption-desorption, SEM and optical microscope, and the gas pressure dependence of their gaseous thermal conductivity was described by Kaganer model with two different pore sizes. The results indicate that the skeleton particle diameter and the pore size are not affected by wetting with alcohol. However, the interfacial area between adjacent skeleton particles increases and the pore size either increases or decreases via water wetting. For the alcohol-wetted material, two different equivalent pore sizes derived from its gaseous thermal conductivity are 70 nm and 300 nm and their contributions to the total porosity are about 82% and 18%, respectively. In case of the water-wetted material, two different equivalent pore sizes deduced from its gaseous thermal conductivity are 30 nm and 60 μm and their contributions to the total porosity are about 58% and 42%, respectively.