Windows have both changed and remained the same since they were first built. Modern windows often keep the pane and slide-open structures of their traditional origins, but also use fiberglass, vinyl and aluminum for stronger frames and tighter seals. What parts specific windows are made of depend on their role and--of course--how much businesses or homeowners are willing to pay for them.
The window frame is the most important part of the window. There are several parts to the frame, and they all work in conjunction to hold the window in place and seal it both inside and outside. The outermost part of the frame is called the casing--there is almost always an interior casing, and often an exterior casing as well. This is a decorative frame that encircles the entire window, and runs into the stool at the bottom of the window, or the flat-based portion of the window frame on which the window rests. Inside the casing are the side jambs, the inner sides of the window frame, and sill, or the exterior lip of the window.
Frames were originally made of wood, but are now available in a variety of natural and synthetic materials. Wood tends to warp or crack over time, so the most efficient windows are made of alternate materials such as aluminum or vinyl. Composite frames are those that use different materials to achieve the best results--the interior frame may be made of wood to give it the proper accent, while the exterior is made of vinyl for better protection. Fiberglass window frames are often the most highly rated when it comes to sealing and can be painted to match the colors of the room.
Traditional window frames are divided into several different panes, which are usually joined by metal or wood strips known as muntins. Muntins can be made from the same materials as the rest of the frames, but in modern windows these strips are usually added in factories as windows are pre-made, and there may not be a wide variety of choices. Windows that slide open have different pane sections that overlap on top of each other, known as sashes. There are upper and lower sashes, depending on which slides over the other. Today, windows can be made of just one pane of glass, though this still increases of the danger of the entire window being ruined if it is damaged.
Different Types of Glass
The type of glass used to created window panes is very important. Older windows used to have only one pane of glass, for instance, but most modern windows have two or more panes, creating a double seal against the air outside, which makes it more difficult to exchange temperatures. Glass can also be reflective, designed to repel the sun's more damaging rays, or built with tinted or sealed layer that lets light in but not heat.
In addition to the frame and panes, there are other features of modern windows that affect their performance. The air trapped between window panes is only one example: some windows come with this air replaced by an inert gas that does not react as readily to outdoor temperatures, sealing in hot or cool air more effectively. There are many other additional features offered by window suppliers to improve the look or function of windows.