Tom Shafer

Fiberglass replacement windows have it all going on

December 03, 2011

Fiberglass is a relatively new material for window frames in the U.S. Due to its resistance to mold, mildew and heat, fiberglass has been commonly used in such diverse products as boat hulls, hospital showers and meat prep areas, but its potential for windows was largely ignored. However, the same qualities that make it perfect for other applications also make it an ideal choice for windows, especially in damp, coastal areas.

If you're looking for a product to satisfy LEED applications, fiberglass is it. Designed with various hollows that trap air like vinyl window frames, fiberglass lineals are able to provide nearly as much insulation as wood frames. Their manufacture, however, consumes much less energy than vinyl lineal production.

In a process called "pultrusion" fiberglass lineals are pulled through a die, and at the same time, encased in a heat-set resin. As a result, they are extremely strong, and in addition to the characteristics mentioned above, highly resistant to all of the following:

  • Scratches (if painted properly)
  • Dents
  • Rot
  • Corrosion

Fiberglass windows give you unlimited color options

Because fiberglass is a stable material with a very low coefficient of expansion, color choice is virtually unlimited. Frames are available with either a powder- or solvent-based coating. Popular colors consist of the usual architectural favorites, like those in Pella's Impervia line--white, brown and tan. Marvin's Infinity product line made of Ultrex® fiberglass is offered from the factory in white, ivory, cashmere, gray, brown and bronze but can be painted any color. Both Marvin and Milgard offer a wood clad interior option that can be stained in most any wood tone.

Amazing strength coupled with energy savings

Perhaps one of the most impressive qualities of fiberglass windows is their strength. Serious Energy, a supplier of commercial windows, is a pioneer in fiberglass window distribution. Their commercial-grade fiberglass windows have earned Heavy Commercial certification from American Architectural Manufacturers Association (AAMA) and a Commercial Window (CW) rating of 100 for their demonstrated strength and water resistance. Residential fiberglass windows are made from the same materials, so if it's strong enough for commercial applications, you know it is strong enough for your home.

Last but not least, the thermal performance of fiberglass makes it the perfect platform for high energy-saving glass. Fiberglass boasts 800 times less thermal conductivity than aluminum. The following chart shows a U-value comparison of various window materials:

Compare thermal value of fiberglass to other replacement window materials

Despite their obscurity here in the U.S., fiberglass windows have been manufactured and used in Canada for years. Enjoy all the advantages of this "new" window material that's been broken in by our neighbors to the north.

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.

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