It is easy to see why vinyl windows now make up about two-thirds of all window sales in the United States: They are less expensive than wood, they are impervious to moisture, they don't rot, and they don't need to be painted. In this article, contributing editor Martin Holladay addresses the important issue of how vinyl windows will look and perform when today’s homes become historic. He states that vinyl windows are better made than they were 30 years ago, attributing this in part to a certification program launched in 1985 by the American Architectural Manufacturers Association. In order to become certified, windows must pass tests for impact resistance, dimensional stability, heat resistance, weight tolerance, and colorfastness. Still, a window is only as good as its installation and maintenance, so Holladay provides a list of tips to help ensure that these windows perform as they are designed to do. Finally, Holladay explores the three phases of vinyl-window construction—formulation, extrusion, and fabrication—and takes a look at vinyl-clad windows.