The corners of the window frame and sashes should be fusion-welded (heat-welded) for a weathertight construction. Beware of windows with mitered corners screwed together or chemically welded corners, as they may decline in performance over time. You’ll also want to take a look at the vinyl extrusions in the window frame and sash. At a quick glance all vinyl windows may look similar, but there can be dramatic differences in the quality of the vinyl used. Some windows, built with lower-quality vinyl that has a dull blue or gray cast, can become brittle over time. Our manufacturer’s windows are constructed with premium vinyl extrusions to ensure the frame and sashes provide long-lasting beauty and performance.