Hy-Lite Block Windows combine the beauty of glass block with the quick and easy installation of a standard window. Constructed of lightweight acrylic blocks, Hy-Lite windows are fully prefabricated and glazed units. Because there's no mortar, there's no mess, no delays, and no headaches. Hy-Lite uses the highest quality acrylic for its blocks. This acrylic won't yellow and resists scratching.