Before you purchase a new vinyl window, make sure it has a certification from the  American Architectural Manufacturers Association (AAMA). Vinyl Windows: Reinforced Interlocking Sash Meeting Rail Double Hung Vinyl Window Example When the 2-Sashes meet in the center of the window, they interlock together to create a tight seal that stops wind, air, water, noise and insect infiltration. They are reinforced with steel, aluminum or a composite, inside the vinyl sash frame for strength and for the cam lock and keeper to mount securely to the sash. Metal Cam Lock and Keeper The metal cam lock and keeper are expertly constructed, stylish and strong. They are the main locking mechanism designed for security and to discourage forced entry. They come in several shapes, sizes and colors. Insulated Glass Units (IGU) or Dual Pane Units engineered for optimal energy efficiency and durability. They are made of 2-sheets of Single Strength or Double Strength glass that are hermetically sealed with ind ustrial strength butyl and High-Performance adhesives. There are several tints available along with inert gases that will help increase the energy efficiency of the overall dual pane unit.