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Fiberglass vs Vinyl Windows

You can face a tough decision when it comes to choosing replacement window materials. Fiberglass and vinyl remain two of the more popular options, but they feature some key differences that set Marvin Replacement fiberglass windows apart. Here’s what to know about fiberglass vs. vinyl windows.

What is Fiberglass? 

Fiberglass window material is made through a process called pultrusion.


The process in which a material gets pulled through a die. The pulling process creates highly concentrated glass fibers to give Ultrex fiberglass superior strength.

Pultruded fiberglass is a thermoset material made through a chemical process. A thermoset fiberglass composite won’t soften or melt in environmental temperatures, making it more resistant to pressure and temperature than vinyl composites.  

Closeup of the construction of Ultrex fiberglass

What is Ultrex® Fiberglass? 

At Marvin Replacement, we go one step further with our proprietary Ultrex fiberglass. Ultrex fiberglass is made by taking thin strands of glass cables and saturating them in specifically compounded resins. The material is pulled through a series of shaping dies that form the sash or frame profiles, passes through a heated die, and then our proprietary acrylic finish is applied. The material is cut with diamond-edge blades.

What is Vinyl? 

Vinyl is a type of plastic made from ethylene and chlorine that when combined make polyvinyl chloride (PVC) resin. It has become the second-most manufactured and sold plastic resin in the world. You can find vinyl in things like old records and vinyl fabric. 

Vinyl Windows 

Vinyl windows remain a popular option for homeowners because of their lower cost, low-maintenance, and easy installation.  

Vinyl windows have some disadvantages, though. Vinyl windows don’t have as long of a lifespan as fiberglass windows.* Plus, vinyl windows can expand in heat and contract in cold which can make them difficult to open and close over the years.  

Why is Ultrex Fiberglass Stronger than Vinyl?  

Comparison of Ultrex fiberglass strength and vinyl windows

Fiberglass vs. Vinyl Value 

Vinyl windows may have a lower price point, but they have a shorter lifespan, and can suffer from expansion and contraction. A shorter lifespan and the contraction and expansion issues could lead to spending more on windows over the life of your home.  

Replacing windows has a 61-68% recovery rate on your investment when you sell your home.  

Fiberglass vs. Vinyl Window Appearance 

Fiberglass windows and vinyl windows can look similar but the properties of Ultrex can make it more resistant to fading and other imperfections.

Ultrex Fiberglass Appearance  

  • Ultrex’s superior strength also means less material is needed for the frame, so you enjoy more glass area to let natural light into your home. 

  • Ultrex’s acrylic finish is three times thicker than competitors, which makes it more resistant to pinholes, scratches, and other imperfections. 

  • Ultrex’s acrylic finish also stands up to the sun—48,000 hours of sun can’t fade the finish. *Average sunlight exposure per 10 years  

  • Our optional EverWood® wood grain interior finish matches the natural look and texture of wood but without the maintenance.  

Vinyl Windows Appearance 

  • Vinyl can offer a range of colors to fit a home. 

  • Vinyl lacks the character that EverWood and wood provide. 

  • Vinyl windows have become so ubiquitous that some homeowners seek different materials to set their homes apart.

Fiberglass vs. Vinyl Window Maintenance 

Both fiberglass and vinyl windows require little to no maintenance. See our tips on how to clean fiberglass windows.

Ready for a Bigger, Brighter View?

Ready to invite Marvin Replacement Ultrex fiberglass windows into your home? Choose from a variety of replacement window options to make your home welcoming.  

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