Michael Anschel is not a fan of vinyl windows, but he loves wood. “Wood requires very little additional energy to manipulate,” says the principal of Otogawa-Anschel Design-Build in Minneapolis. “It is stored carbon, it can be easily handled when its useful life has ended, and it is beautiful.”

But if Anschel had to compromise, he would go with fiberglass.

“I feel better about fiberglass,” Anschel says. “The expansion and contraction of the frame material and the glass are closer, so durability is increased. They are more stable overall, and failures seem less likely.”

Fiberglass windows have been around for a while, but in recent years the product has achieved a higher profile. Because of the many benefits, manufacturers say it’s the perfect material for windows.

“The superior characteristics of fiberglass that make our lives mobile, safer, and convenient are the same qualities that contribute to making a solid, long-lasting window,” says Dave Koester, wood and fiberglass products brand manager at Medford, Wis.–based Weather Shield Windows & Doors. “It’s energy efficient, durable, and doesn’t become brittle. It’s also resistant to water, scratches, dents, and corrosion.”

Strength is one of the most oft-reported benefits of fiberglass. Warroad, Minn.–based Marvin Windows and Doors says its Integrity brand of Ultrex fiberglass windows is as strong as steel and is eight times stronger than vinyl. “In fact, it’s so tough, we have to use diamond-edge blades just to cut it to size,” the company says.

Fiberglass also is a good energy-efficiency option. The Energy Department says fiberglass windows have air cavities similar to vinyl and when “these cavities are filled with insulation, they offer superior thermal performance compared to wood or vinyl.”

So if fiberglass windows are so great, why aren’t they more popular? Cost might be the main reason.

“Because of its durability, fiberglass is the most expensive window material on the market,” says the Seattle-based window dealer Keystone Windows and Doors. In other words, manufacturers charge a premium for the material.

Sizes and features are also limited. John Kirchner, public relations manager for Marvin, confirms that there are limitations “due to the strength and durability of the fiberglass making it difficult to bend and shape.” Round tops or radius windows are not possible, he adds.

Still, if you can work around those constraints, fiberglass offers features and attributes that your home buyers will love. Moreover, it has “the benefit of being able to mimic the appearance of wood, which improves consumers’ acceptance of the product,” Anschel says.