Studies carried out to improve the thermal insulation of architectural structures are made possible by the development and use of innovative building materials thanks to modern technology. In this study, it was aimed to obtain superior thermal insulation properties by adding silica aerogel powders with excellent thermal insulation ability to plaster (plaster of paris), which is a classic building material. Thus, within the scope of the study, experimental plaster samples were prepared by adding silica aerogel material, synthesized with superhydrophobic properties using commercial casting sand, at low reinforcement ratios of 0 wt%, 0.5 wt%, 1 wt%, 2 wt%, and 5 wt% into the plaster material. After a waiting period of 28 days, thermal conductivity and water absorption tests were performed to examine the effect of superhydrophobic silica aerogel additive on experimental plaster samples and to determine their physical properties. As a result of the experiments, it was observed that increasing the amount of superhydrophobic silica aerogel reinforcement positively affected the thermal conductivity and water absorption properties of the material, and it was understood that the properties of the material could be improved. With the use of superhydrophobic silica aerogel as an additive material to plaster building material, this study provides innovative information to the literature related to architectural building materials and applications.