Like many building product categories, window manufacturers are pumping out composite units that combine great performance and authentic looks. Composite windows boast a balance of materials with low maintenance, moisture resistance, and energy efficiency. Many also offer the look of wood.

The term composite window isn't easy to define because it means different things to different manufacturers. Some units are made up of multiple materials, such as Traco's aluminum and vinyl windows. Others incorporate fiberglass or wood composite materials. CertainTeed's Haverford replacement windows have an extruded wood-fiber composite on the frame and sash, while Marvin's Integrity windows feature an exterior cladding of glass fibers bonded with a liquid polyester resin.

One recent entry is MI Home Products' revamped PrimeCel windows. Made with Micron--a vinyl-wood composite with a co-extruded capstock material--they combine the look of a wood window, the durability of vinyl, and a high-end finish.

While technically a vinyl window, Superseal's new cellular PVC unit is comparable to composites in its performance. It offers a paintable and stainable surface and is 200 percent more energy efficient than standard vinyl and 50 percent more efficient than wood.

While sales of composites are still comparatively small, the Window and Door Manufacturers Association reports that sales are growing steadily. As manufacturers continue to experiment with materials, expect the category to continue to improve and grow.

Courtesy MI Home Products

Prime time view: Constructed of 100 percent cellular composite, this PrimeCel window combines the look of a traditional wood window without the rotting, the durability of a composite, and the design flexibility of three different exterior profiles. The window comes factory pre-finished and can be painted. MI Home Products. 717-365-3300.

The vinyl frontier: Made of cellular vinyl, this window offers the texture and appearance of pine with the ease of a maintenance-free unit. According to the firm, the unit insulates 50 percent more than wood and 200 percent more than hollow vinyl. The interior wood finish can be painted or stained. Superseal Mfg. 888-639-8469.

Courtesy Peachtree

Composite sketch: Image composite windows combine a solid vinyl composite sash and an aluminum-clad frame, which allows for easy installation, reliable thermal performance, and low maintenance, says the maker. The windows come with colonial white or driftwood exteriors with 3/4-inch insulated glass. Peachtree. 800-732-2499.

Wood look: Made with vertical grain Douglas fir on the inside and fiberglass on the outside, WoodClad composite windows offer enhanced durability, thermal performance, and low maintenance, the firm says. Window exteriors feature the look of wood and include a baked-on finish that will not crack or peel. Milgard. 800-645-4273.