Abstract: Borosilicate glass (K9 optical glass) and polymethyl methacrylate (aviation organic glass, PMMA) are core transparent materials for aerospace, optical instruments and sealed-cabin applications. Their service scenarios involve complex working conditions such as dynamic loads, temperature-humidity alternating cycles, and drastic pressure changes. There are significant differences between the two materials in key performance parameters, including thermal expansion coefficient, elastic modulus, surface energy and environmental adaptability, which directly affect the long-term reliability and stability of sealing interfaces. In this study, a systematic experimental scheme was adopted to compare the static sealing performance and interfacial durability of the two materials under standardized environmental conditions. The helium leakage rate was quantified, and the inherent mechanism between material microstructure and macroscopic sealing performance was analyzed. This work aims to provide solid experimental data support and theoretical references for material selection, process optimization and reliability design of sealing structures in aerospace, precision instruments and other fields.