Inward-opening system windows are widely used in Chinese homes; the sash opens inward and, when closed, the hardware presses the gasket to form a seal. Sealing quality directly determines indoor thermal insulation, soundproofing and rain protection. Yatton treats sealing as the first line of defence of the whole window. Profile structure is the basis of sealing: system windows use multi-chamber designs, and the equal-pressure chamber drains infiltrating moisture in an orderly way, reducing the pressure of rainwater penetrating indoors; by contrast ordinary single-cavity profiles have obviously poor water tightness. When choosing, pay attention to profile wall thickness, chamber count and the thermal-break strip material, which directly affect strength and insulation. The material and lap joint of the sealing gasket also matter: EPDM gaskets have good weather resistance and lasting resilience and suit long-term use; the gasket should be welded into a continuous loop at corners or use dedicated joints to avoid breakpoints. Hardware provides the pressing force; multi-point locking makes the force around the sash even, and insufficient lock points leave gaps in the middle of the sash. Installation is often the underestimated step: window levelling, the connection between frame and wall, and the density of foam filling all affect the final seal. After installation, do a water-spray test and check the feel of opening and closing to confirm no leakage or sticking. The performance of an inward-opening system window is the combined result of profile, gasket, hardware and installation; any weak link affects the whole.