Silica aerogels are often deployed as solid desiccants in enthalpy wheels used for dehumidifying ventilation air in airconditioning systems. These materials have good adsorption and desorption characteristics, but microstructure affects their moisture diffusivity. As the performance of desiccant systems depends on diffusivity, it is important to select a preparation method providing the desired aerogel microstructure for enhanced dehumidification performance. A study is described in which the structure of silica aerogels prepared by the Sol-Gel process is analyzed. The same precipitator (TMOS-Tetra methyl orthosilicate) and solvent (Methanol) are used to prepare all samples. It is found that density and microstructure are highly dependent on the catalyst used in the Sol-Gel process. Dynamic vapor sorption experiments are conducted to determine diffusivity. Microscopic images are analyzed to discern the structure and to relate it to corresponding adsorption or desorption performance parameters.