There are different types of materials used to make replacement window frames. The material that is used has a huge factor not only on the window's aesthetics, but also on its performance and durability.

With all the information out there, we understand it can be confusing to know what is the best replacement window on the market. But we want to make window-shopping simple.

Today, we focus on two window materials - Fibrex® and fiberglass. But not just any fiberglass - Ultrex® fiberglass.

They sound similar, but how different are they?

What is Fibrex®?

Fibrex® is a composite material made up of 40% wood and 60% plastic. It is a thermoplastic material, which is a substance that becomes pliable on heating and hardens on cooling, and then it's able to repeat this process.

Fibrex® is not fiberglass.

What are the pros of Fibrex® windows?

  • Fibrex® windows do not need to be painted, nor will they rot.
  • Fibrex® can be formed into many different profiles.
  • Fibrex® is twice as strong as vinyl.

    • What are the cons of Fibrex® windows?

  • Fibrex® windows can bow and warp.
  • Despite being twice as strong as vinyl, Fibrex® windows still have thick frames, which means it cuts into your daylight and views.
  • Fibrex® windows often come with double locks and double lift rails on double-hung and slider windows, which create a cluttered view.
  • As mentioned above, Fibrex® is thermoplastic. These types of materials have low melting points, which means they cannot withstand as high temperatures as thermoset materials.
  • Fibrex® (the window frame material) and the glass are made from two different components; therefore, they expand and contract at different rates. As the frame expands and contracts, the seal that protects the two panes of glass can become compromised, causing moisture to build up between the two panes, leading to seal failure and other issues.
    • Thick frames prevent more daylight and bigger views.
    Double locks and double lift rails create an unsightly appearance.

    What is Fiberglass?

    Fiberglass is a type of fiber-reinforced plastic using glass fibers. These fibers can be arranged differently in the manufacturing process.

    Enter Infinity from Marvin's Ultrex® fiberglass. This manufacturing process is what separates their product from just any type of fiberglass. Thin strands of strong glass cables are saturated with compounded resins. These cables are then pulled through a heated die and cut with diamond-edged blades to form the Ultrex® material. Lastly, a proprietary acrylic finish is applied that prevents Ultrex® from needing any painting, although it still remains a paintable product if desired.

    Ultrex® is a thermoset material, meaning once their components and physical properties reach a certain temperature and cure, they become set. Their properties can't be melted back down or restored to their original state. This means doors and windows made of Ultrex® fiberglass will not melt or lose their true shape, even when exposed to extreme temperatures of up to 285° F. It also means they perform under all types of weather.

    What are the pros of Ultrex® fiberglass windows?

  • Ultrex® fiberglass can be formed into many different profiles, including shapes.
  • It is 8x stronger than vinyl and 3x stronger than Fibrex®. This means the replacement window frames are more narrow, allowing for more daylight and bigger views than other replacement windows on the market.
  • Because of this strength, Ultrex® fiberglass windows only have one lock on their double-hung and slider windows, creating a clean and obstructed view.
  • The Ultrex® fiberglass replacement window frame and the glass are both made from the same basic material - silica sand. This means that they expand and contract at nearly the same rate, ensuring the windows stay tight and true and making the Infinity window resistant to leaks, seal failures and stress cracks.
  • The Ultrex® fiberglass proprietary finish is 3x thicker than the competition. This means no sanding, scraping or painting is required. Also, it will not rot.

    • Images property of Infinity from Marvin Replacement Windows.

    What are the cons of Ultrex® fiberglass windows?

    Because of its performance, it is a premium product and is therefore more of an investment than other replacement windows. However, it is a product that it is Built for Life®, and is worth considering when compared to the money spent on maintaining and upkeeping other types of windows.
    Thin frames help preserve daylight and create bigger views than other replacement windows.

    Fibrex® vs. Fiberglass. And, more specifically, Fibrex® vs. Ultrex®.

    As you can see, the most common similarities the two have are in their names and phonetics. Beyond that, it is clear to see the differences between Ultrex® and Fibrex® replacement windows.

    To learn more about replacement windows and what is the best window to install, contact us today to schedule your free consultation.

    Fibrex® is a registered trademark of Andersen Corporation. Ultrex® is a registered trademark of Marvin Lumber and Cedar Co., LLC.