Fibrex vs. Fiberglass
The Advantages and Disadvantages of Fiberglass & Fibrex® Replacement Windows

When it comes to replacing your windows both Fibrex® and fiberglass (Ultrex®) have different properties that give them advantages to standard vinyl windows. Both have a longer lifespan, with better energy efficiency, durability and strength. However, comparing Fibrex® to fiberglass isn’t always easy with so many biased articles floating around on the internet. We sell and install Fibrex® (Renewal by Andersen) windows vs fiberglass (Marvin) replacement windows. To help homeowners understand the differences we’ve put together an article explaining the advantages of each window.

Fiberglass Replacement Windows

The bestselling fiberglass window is made by Marvin. Their replacement windows are constructed using a fiberglass compound called Ultrex®. Ultrex® fiberglass holds strong against vinyl and wood window options.

- Ultrex® fiberglass offers more strength than vinyl, and better energy efficiency. 

- Ultrex® also carries some of the best energy efficiency ratings in the replacement window industry.

- Ultrex® resists sticking, swelling and warping. 

Disadvantages of Fiberglass Replacement Windows

- Fiberglass frames are painted and may need regular maintenance.

- Fiberglass can only be made into straight lineals.

- Fiberglass is a thermoset material and cannot be reformed into new profiles.

- Few color choices & optional features.

- Higher price compared to vinyl.

Fibrex® Replacement Windows

Fibrex® was invented by the Andersen Window Corporation. Fibrex® is a revolutionary composite material that combines the strength and stability of wood with the low-maintenance features of vinyl.

Fibrex® has advantages like narrower frames allowing for more glass space.

Fibrex® offers more strength than vinyl and a better energy efficiency.

Fibrex® windows never need to be painted, nor will they ever warp, rot, flake blister or peel.

Compared to fiberglass windows, Fibrex® can be formed into many different profiles. Fibrex® material can be extruded into any kind of window – including curved and specialty windows, unlike fiberglass that’s restricted by straight lineals and profiles. This helps to preserve the unique architecture and beauty of your home.

Since Fibrex® is formed using real wood, it also retains a more natural wood look compared to fiberglass windows.

Disadvantages of Fibrex®

Fibrex is the best composite material for use in windows today. As such, fibrex-based windows tend to have a higher sticker price compared to other materials used for windows. 

Fibrex® used to be a big question mark for some people because it was such a new product. However, Fibrex® has proven it can stand the test of time. Renewal by Andersen recently pulled a batch of original windows from the home they had been installed in more than two decades ago.* After more than 20 years in a real family home, facing real weather the windows still looked brand new, and they still opened and closed as easily as the day they were installed.**

*Based on testing of 10 double-hung units 20 years after installation
**Testing per ASTM E2068

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