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Standalone Strength
The power of Ultrex® fiberglass
What is Ultrex fiberglass?
Ultrex is a pultruded fiberglass material used in Infinity windows and doors, engineered for exceptional strength, durability, and long‑term performance. It resists warping, expanding, and contracting in extreme temperatures, making it more stable than vinyl or composite materials. Ultrex also delivers excellent energy efficiency and low maintenance, making it a reliable choice for replacement windows.
Ultrex is a custom reinforced fiberglass composite used to create windows and patio doors. Ultrex fiberglass has superior strength, stability, and durability to other window and patio door materials.
Infinity by Marvin fiberglass windows & patio doors
Engineered to outperform
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Ultrex fiberglass vs. vinyl
Over time, vinyl warps and shifts, making it difficult to open and close your windows. The strength of fiberglass ensures they perform as smoothly on day 10,000 as the day they were installed.
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Ultrex fiberglass benefits
Withstands 285°F
Weathers the extremes
The strength of Ultrex combined with our proprietary acrylic finish means your frames can resist warping, bending, flexing, and fading — even in the most extreme conditions.
3x thicker
Finished to last, beautifully
Dent, chip, scratch, chalk, and fade resistant, our proprietary acrylic finish is 3x thicker than others on the market, delivering a sleek, smooth look that stands up to the test of time.
87% less expansion
Maintains leak-proof fit
Expanding less than both vinyl and Fibrex®, Ultrex frames stay tight and true to your glass panes, maintaining an energy-efficient seal year after year.
We are extremely pleased with our new windows. We had eight windows and one patio door replaced. The stained EverWood® matched our oak trim nicely. Windows seal well and are easy to operate. Workmanship was excellent. Attention to detail was evident. Job well done!”
Joe and Jean R.
Minnesota Homeowners
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Power of numbers
From ordinary to extraordinary
8x
Ultrex is 8x stronger than vinyl
The strength of fiberglass stands the test of time so you get more expansive views — built to last.
3x
Ultrex fiberglass is 3x stronger than Fibrex®
Made using millions of fiberglass strands, Ultrex is stronger than the vinyl/wood composite used by competitors.
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How our strength stacks up
Made with 100% fiberglass versus the blend of vinyl and wood fibers used in Fibrex®, Ultrex protects the integrity of your home with superior bend and flex resistance. This strength is measured in KSI. For context, 1 KSI is equivalent to 1,000 PSI. The graph shows how these materials stack up under pressure.
Stunning, inside and out
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Expand your view
With more strength per square inch, Ultrex delivers expansive views with slimmer profiles.
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Customize your style
A range of timeless finish options can also be painted to complement your home without compromising the protective, low-maintenance fiberglass material.
How we do it
Harnessing the strength of fiberglass
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Frequently asked questions
Replacement windows with multiple panes of glass and a gas fill, along with Low-E glass coatings are considered the most energy efficient. The window frame material can play a role in energy efficiency with materials like fiberglass providing better insulation than other window materials. Window with two or more panes contain a gas fill, often an inert, non-toxic gas, that adds a layer of insulation. Low-E coatings help reflect solar heat to improve energy efficiency.
Infinity by Marvin fiberglass windows have greater durability and strength than vinyl windows. Our Ultrex fiberglass has 8x the strength of vinyl to resist warping and seal failure. Ultrex fiberglass has more stability than other window materials and expands 87% less than vinyl. Plus, we offer a fade-resistant finish.
Your questions answered
Plan your replacement with confidence
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Why choose Ultrex fiberglass for your windows and doors?
Wood? Vinyl? Fiberglass? How do you choose the best material for your new windows?
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Vinyl vs. fiberglass replacement windows
When replacing your windows and doors, choosing the right material plays a key role in the process.
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Fiberglass vs. wood windows: What’s the difference?
One of the most important decisions when replacing your home’s windows is choosing the right material.
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Best windows and doors
From materials to installation, it is important to do your research before making such an important purchase for your home.
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How to choose new windows for your home
When it comes to replacing windows, it's normal to feel a bit lost about where to begin.
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