1. Inner sash superposition materials are designed with handles and on a double-hollow basis. And window structure is even firmer by virtue of the design of windproof superposition; 2. Tough, durable and luxury crescent-shape window locks uniquely manufactured by Fen An company are adopted to naturally obstruct the noise of wind; 3. The structure of high / low double reflux troughs is adopted to create high fall between internal and external water levels; 4. The inner frame closely sticks to the lower horizontal airtight adhesive tape of the outer frame; 5. Specially assembly include Lock bumper, Burglar alarm, Crescen lock, Double felt strips, Multifunctional drain hole, Waterproof shim, with multi-protection.