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Best Fiberglass Windows

Browse the top five best fiberglass windows and models from top window manufacturers. It can be difficult to figure out which is the best fiberglass windows for your project, so we have made it easier for you by listing the top five fiberglass windows we would recommend based on customer reviews. Everyone has different opinions so we have also included the links for you to visit the pages on each of the windows and read the reviews for yourself to help you make an informed decision.

Marvin Integrity

Marvin Integrity are considered a solid fiberglass window and a popular choice. They come with two profiles available, the All Ultrex and the Wood Ultrex. The All Ultrex windows have fiberglass inside and out while the Wood Ultrex has wood on the inside and fiberglass on the outside, making them visually appealing. You can get casements, awnings, bow, bay, sliders, round top, double hungs, French doors and polygon windows in the Marvin Integrity design - but note that these windows don't offer a wide selection of options and sizes.

Marvin Infinity

Marvin Infinity model is another of the best fiberglass windows chosen by customers and contractors alike, they are considered the top end of the fiberglass market (but not as expensive as a wood clad option) and they are visually appealing in design. They offer the durability of fiberglass without any maintenance, they come with great energy efficiency and they look like wood. These windows have a good selection of colors and options available but because you can only get them in a fiberglass frame they are slightly higher priced than the Marvin Integrity.

Milgard Ultra

The Milgard Ultra is a top choice for new constructions and replacements. The frames look like wood and you can barely tell the difference except they are fiberglass. The Milgard Ultra DH was removed from the market for three years because of design problems, however the window has come back - some installers are still tentative when using them. They had problems with water and air flow through the windows, but they offer a fantastic warranty and are well known and regarded in the industry.

Pella Impervia

The Pella Impervia is a fiberglass windows because that offers lots of custom features and offers a good frame profile. While they are considered more on the expensive side, Pellas remain popular. Some contractors consider this window to be overrated when compared to the Marvin windows These windows come as casements or double hungs.


Serious windows went through financial difficulties and sold off their window division. Prior to this, the windows came in four series, the 525, the 725, the 925 and the 1125. They were manufactured in Sunnyvale and offered an energy efficiency window with an R-9 value. They claimed to be one of the most energy efficient choices available on the market, but their price was cost prohibitive and they didn't have many distributors. For additional pricing using our window replacement cost estimator, click here.

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