WOOD. Wood has been a traditional material for windows for centuries. There are some advantages to wood windows. They can be painted or stained to match your interior décor, they can look as nice as furniture, and they fit well into historic renovations. The downside of wood is that it is susceptible to damage from excessive moisture (it can warp or rot), excessive dryness (it can crack or split) and it does require some type of sealing to make it last long term. The wood windows on the market today are primarily designed for new construction. With new construction windows, you install the window in a new opening, and install new exterior and interior trim. New construction windows work well when you are gutting the home, since they generally are made standard sizes, and you must make your openings fit the stock window sizes available from the manufacturer. Some manufactures will make custom sized windows, although this can add substantially to the cost per window. You will also have the cost of buying and installing the new trim. There are a few regional manufactures that make custom size wood windows to order as their normal procedure (for example TrimLine Windows). Although these may be higher end windows, you will not pay custom size charges. These windows are true "pocket replacement windows" meaning they are designed to fit into the 3 ¼ inch space where the old wood sashes were removed from. With this type of installation, you will not be forced to replace the trim on the interior and exterior. Now you can get the advantages of a wood window without the installation problems.
ALUMINUM. Aluminum was used on many low-end builders grade windows in the past 50 years. They were strong, inexpensive and did not require painting. Today, they are considered the least effective windows at keeping the heat in your home since they conduct heat at a rate over 1000 times faster than wood or vinyl. They are primarily used today for commercial applications. Removing aluminum windows from your home and installing energy efficient windows in their place can cut heating costs by as much as 50%.
VINYL. Vinyl is rapidly becoming the material most used for replacement windows. Manufactures have been very creative in producing a wide variety of different color combinations, woodgrain looks, even paintable and stainable synthetic surfaces that will last a lifetime once a finish is applied. The newest pre-finished wood-grained windows are almost indistinguishable from actual stained wood. So if you like the look of wood, there is a good chance you can have a window that will please the eye and require no maintenance at all.
CELLULAR PVC. This is one of the latest improvements in window construction in the last 20 years. A cross section of this material looks like vinyl on steroids. It is produced by a slower extrusion process, which allows the PVC to expand and become structurally stronger than regular vinyl. In fact, it is 140% stronger than vinyl, so especially for large windows, it the material of choice. It is a 214% better insulator than vinyl and it is a 60% better insulator than wood. Some manufacturers offer pre-painted exterior, to give the homeowner the ability to compliment the exterior color of their home.
FIBERGLASS. Fiberglass windows are fairly new to the market. They are made with some post consumer glass recycled into what are called "pultrusions" This is similar to extrusions, but is pulled through the die instead of being pushed through the dies. High cost and low availability have made this product rare in the marketplace. It has some advantages such as strength and it is paintable. It is used in less than 1% of windows today.
COMPOSITE. Composite material is made by mixing ground up vinyl with sawdust and combining the resultant mixture with epoxy binders. The result is a strong material resistant to wear and tear. Most windows that use composites in them use them in conjunction with other materials. Composites are relatively new on the market. They are generally much more expensive due to the low market share. Only time will tell if they are accepted in the marketplace.
In conclusion, vinyl and cellular PVC have the most rapid growth in the window replacement products used today. The options and colors available, as well as affordability make them the most popular materials to replace your windows. They have proven longevity, with great support from dealers and manufacturers. Check with a professional window company to have them review your project, and beware of high pressure sales tactics.