Fenestrelle Expanding Window Screens feature a strong, white, powder coated, aluminum box frame and fiberglass screen that will hold up to the harshest of conditions. Weather stripping top and bottom adjusts to rough surfaces and keep small critters from sneaking in. How to Use: Open Window Insert Fenestrelle Screen Expand to fit width of window Close window until it contacts top of screen. Screen expands horizontally in one direction and vertically in one direction.