What Are Fiberglass Windows?

You've probably dealt with traditional window headaches before. Maybe it's those wooden frames that looked gorgeous when installed but now have paint peeling off and signs of rot. Or perhaps it's cheap vinyl windows that seemed like a bargain until they warped and created gaps.

Fiberglass windows were designed to solve these common problems. Unlike wood, fiberglass won't rot, swell, or need regular painting. Unlike vinyl, it holds its shape through temperature extremes. And unlike aluminum, it won't conduct cold into your house in winter.

At Southwest Exteriors, we sell both fiberglass and high-quality vinyl windows, like Provia (in fact, we sell a quite a lot of them!), but today we're going to talk all about fiberglass windows - what they are, why they outperform other windows, and when you might want to choose them for your home.

Let's dive in.

What Are Fiberglass Windows?

Fiberglass windows are essentially window frames made from thousands of glass fibers embedded in a resin material – think of it as super-strong plastic reinforced with glass.

The way these windows come to life is pretty fascinating. Manufacturers use a process called pultrusion – where they pull glass fibers through a bath of resin and then through heated dies that shape and harden the material. This creates long, straight frame pieces with consistent properties from end to end.

After that, these pieces get precisely cut and assembled with specialized corner joints to form the window frames. The surface can be produced with different finishes – smooth surfaces ready for painting, factory-applied colored finishes, and even options that look and feel exactly (and we mean exactly) like real wood.

Benefits of Fiberglass Windows

After installing hundreds of these windows over the years, we've seen firsthand how they outperform traditional materials in several key areas:

Superior Insulation and Energy Efficiency

Fiberglass windows are energy-saving powerhouses. The material itself is a poor conductor of heat and cold, which means less temperature transfer between your home and the outdoors, but the window's superior energy efficiency primarily comes from it's ability to withstand expansion and contraction. Most windows expand and contract a great deal with temperature changes, which can create air leakage. Of all window types, fiberglass expands the least, which translates to energy savings. 

Strength and Durability Advantages

Fiberglass is seriously tough stuff. It's about eight times stronger than vinyl and doesn't weaken over time like wood can. This strength allows for slimmer frames and larger glass areas, maximizing your view and natural light.

The durability is impressive too. We've installed fiberglass windows that have weathered multiple decades without significant deterioration. Unlike vinyl that can become brittle with age and UV exposure, fiberglass maintains its structural integrity for its entire lifespan. For most homes, these are the last windows you'll ever need to install.

Low Maintenance Requirements

If you've ever had to scrape, sand, or repaint wood windows, you'll love fiberglass. These windows require virtually no maintenance beyond occasional cleaning. There's no risk of rot, rust, or corrosion, and you won't need to repaint them every few years to keep them looking good.

Weather Resistance and Performance in Extreme Conditions

Whether you're dealing with blazing heat, freezing cold, or coastal salt spray, fiberglass windows handle the punishment better than any other material we've worked with. Like we mentioned earlier, they don't expand and contract much with temperature changes (actually, they expand at almost exactly the same rate as the glass itself), which means the seals stay tight and you don't get air leaks.

Aesthetic Versatility and Design Options

Don't think you're sacrificing looks when you choose fiberglass. These windows come in virtually any style and color. They can also be painted (something you can't do with vinyl), and many manufacturers offer fiberglass windows that look virtually identical to traditional wood windows. Infinity from Marvin, for instance, has a line called Everwood, that not only looks, feels, and even smells like real wood, but it can be stained like real wood (something you can't do with other fiberglass windows). 

We've installed fiberglass windows in everything from modern homes to historical renovations, and they complement any architectural style beautifully.

Comparing Fiberglass to Other Window Materials

OK, now let's examine how fiberglass measures up against the traditional options of vinyl, wood, and aluminum.

Fiberglass vs. Vinyl

Related article: Vinyl vs Fiberglass Windows: Cost, Durability, & More

Fiberglass and vinyl windows represent the two most popular modern window options, but they differ significantly in several important aspects:

Strength: Fiberglass is approximately eight times stronger than vinyl, allowing for slimmer frames and larger glass areas without compromising structural integrity.

Thermal Performance: While both materials offer good insulation, fiberglass maintains its shape in extreme temperatures, ensuring consistent energy efficiency. Vinyl expands and contracts quite a bit more with temperature changes, potentially compromising window seals over time.

Longevity: Fiberglass typically lasts 50+ years, while vinyl windows generally have a 20-30 year lifespan. Vinyl is susceptible to UV degradation and can become softer over time.

Aesthetics: Fiberglass can be painted any color and offers a more authentic wood-like appearance. Vinyl cannot be painted effectively and usually (though not always) has a more artificial appearance.

Fiberglass vs. Wood

Wood windows have been the traditional choice for centuries, but fiberglass offers several advantages:

Maintenance: Wood requires regular maintenance including painting, staining, and sealing to prevent rot and warping. Fiberglass needs virtually no maintenance beyond routine cleaning.

Moisture Resistance: Fiberglass is impervious to moisture damage, unlike wood which can rot, swell, or warp when exposed to humidity and precipitation.

Stability: Fiberglass maintains its dimensions in varying weather conditions. Wood expands and contracts with moisture and temperature changes.

Pest Resistance: Fiberglass is immune to insect damage, while wood can be susceptible to termites and other wood-boring pests.

Appearance: Modern fiberglass windows can closely mimic the look of wood, and some premium products can even be stained like wood.

Fiberglass vs. Aluminum

Aluminum has long been valued for its strength, but fiberglass offers significant advantages:

Thermal Efficiency: Fiberglass provides superior insulation, as aluminum readily conducts heat and cold. Aluminum windows typically require thermal breaks to improve efficiency, while fiberglass is naturally insulating.

Condensation Resistance: Fiberglass frames resist condensation buildup in cold weather, while aluminum frames often develop condensation due to the temperature differential.

Corrosion Resistance: Fiberglass will never corrode, while aluminum can develop corrosion issues, particularly in coastal environments.

Noise Reduction: Fiberglass provides better sound insulation compared to aluminum, which can transmit noise more readily.

Environmental Conditions: While both materials handle extreme weather well, aluminum can become uncomfortably hot to touch in summer, whereas fiberglass remains at a more moderate temperature.

Comparison Chart of Key Features

Fiberglass Windows: Cost Considerations

There's no getting around it, fiberglass windows come with a higher upfront price tag than some alternatives. So if you're on a budget or you're planning to move out of your home, fiberglass may not for you. But as with most home improvements, you need to look beyond just the initial receipt to understand their true cost.

Initial Investment vs. Long-Term Value

When we're working with homeowners on a budget, we often talk about the long-term cost of ownership. Fiberglass windows typically cost about 10-30% more than vinyl windows up front. 

But fiberglass windows often last twice as long as vinyl. So while you're replacing those vinyl windows in 20 years, your fiberglass windows will still be going strong. Plus, fiberglass windows tend to maintain their appearance and functionality better over time, which helps preserve your home's value.

Energy Savings Potential

Now let's talk about the money flowing out of your home through inefficient windows. Fiberglass windows can significantly cut your energy bills, often saving 10-15% on heating and cooling costs compared to older windows or less efficient materials.

For a typical home spending $2,500 annually on heating and cooling, that's a potential savings of $250-375 per year.

Another thing to consider is that utilities and government programs offer rebates for energy-efficient windows too, which can help take some of the sting out of the initial purchase. Be sure to ask about ENERGY STAR certified fiberglass windows, which qualify for many of these incentive programs.

Fiberglass Windows: Installation Considerations

When it comes to installing fiberglass windows, there are some important factors to consider before diving into the project. We've installed hundreds of fiberglass windows over the years, and we've seen firsthand what makes for a successful installation.

Professional vs. DIY Installation

We're often asked if homeowners can install fiberglass windows themselves. While it's technically possible for an experienced DIYer to handle a straightforward replacement, we generally recommend professional installation for fiberglass windows. Here's why:

Fiberglass windows are a premium product, and proper installation is crucial to realizing their full benefits. Professional installers have the specialized tools, experience with the specific products, and knowledge of current building codes. They also know how to properly seal and insulate around the windows to prevent energy loss and moisture problems.

For DIY enthusiasts determined to tackle the project, we suggest starting with just one window in an easily accessible location. Manufacturer installation instructions must be followed meticulously, as improper installation can void warranties. Remember that fiberglass is extremely strong but can be damaged by improper handling or installation techniques.

The cost difference is worth considering too. While professional installation adds more to your project cost, it includes labor warranties and often the manufacturer's full warranty coverage. DIY installations might save money upfront but could cost more if problems arise later.

Are Fiberglass Windows Right for Your Home?

After exploring the benefits, costs, and environmental aspects of fiberglass windows, the big question remains: are they the right choice for your specific home? Let's look at where fiberglass windows shine brightest and what factors might influence your decision.

Best Applications for Fiberglass Windows

Fiberglass windows work exceptionally well in several specific situations:

Coastal and harsh environments: If your home faces salt spray, extreme temperatures, or intense UV exposure, fiberglass provides superior durability compared to other materials. We've installed fiberglass windows in oceanfront homes where other window materials had repeatedly failed.

Energy-efficient builds: For homeowners focused on energy efficiency—whether building a new high-performance home or retrofitting an existing one—fiberglass provides excellent thermal performance. The material's inherent insulating properties make it ideal for passive houses or net-zero energy homes.

Low-maintenance preferences: If you want to install windows and then essentially forget about them, fiberglass is hard to beat. Unlike wood windows that need regular refinishing or vinyl windows that may degrade over time, fiberglass requires minimal attention to maintain its performance and appearance.

Large window openings: The strength of fiberglass allows for larger glass areas with slimmer frames. For contemporary homes with large windows or for maximizing views and natural light, fiberglass provides the necessary structural integrity without bulky frames.

Long-term homes: If you plan to stay in your home for many years, the longer lifespan and durability of fiberglass makes the higher initial investment more worthwhile. The long-term savings on energy, maintenance, and replacement costs really add up over decades.

Considerations for Different Home Styles and Climates

Historic homes: For historic preservation, fiberglass windows are available with traditional detailing that can closely match original wood windows while providing modern performance. However, some historic districts have specific requirements, so check local regulations before proceeding.

Contemporary homes: The clean lines and minimalist frames possible with fiberglass complement modern architectural styles beautifully. The ability to specify large glass areas with narrow frames makes fiberglass a favorite for contemporary designs.

Cold climates: In regions with harsh winters, fiberglass windows prevent heat loss through the frames and maintain their tight seals despite temperature fluctuations. We often recommend fiberglass for northern climates where heating costs are a significant concern.

Hot climates: Similarly, in hot southern regions, fiberglass helps keep cool air in and hot air out. The material doesn't soften or warp in extreme heat like some vinyl products can.

Humid environments: In areas with high humidity, fiberglass won't swell, rot, or grow mold like wood can, making it an excellent choice for bathroom windows or homes in naturally humid regions.

Questions to Ask When Shopping for Fiberglass Windows

When evaluating fiberglass window options, we recommend asking these key questions:

What is the warranty coverage? Look for comprehensive warranties that cover both materials and installation. The best manufacturers offer 20+ year coverage on fiberglass frames and 10-20 years on insulated glass units.

How is the window constructed? Ask about corner joints, wall thickness, and weatherstripping. Quality fiberglass windows have mechanically fastened corners (not just glued), substantial wall thickness, and durable weatherstripping systems.

What are the energy performance ratings? Request the specific U-factor, Solar Heat Gain Coefficient (SHGC), and air leakage ratings. Lower U-factors indicate better insulation value, while appropriate SHGC depends on your climate.

What options are available for glass packages? Different glass options optimize performance for different climates. Triple-pane glass, low-E coatings, and gas fills can enhance performance in extreme climates.

Are the windows ENERGY STAR certified for your climate zone? This certification ensures the windows meet minimum energy efficiency standards for your specific region.

What experience does the installer have with fiberglass specifically? Fiberglass is somewhat harder to install than vinyl. Make sure your installer has specific experience with fiberglass products.

What finish options are available? Ask about standard colors, custom color options, and whether the windows can be painted later if you change your color scheme.

Can I see samples of the actual product? Operating a sample window can tell you a lot about build quality and functionality that you can't determine from a brochure.

How long will the project take? Fiberglass windows are often custom-manufactured for your specific openings, which can mean longer lead times than stock vinyl windows.

By carefully considering these factors and asking the right questions, you'll be well-positioned to decide whether fiberglass windows are the right investment for your home. While they aren't the cheapest option upfront, many homeowners find that fiberglass windows provide the best long-term value and performance for their specific needs.

Making the Right Window Choice for Your Home

Fiberglass windows represent an impressive balance of durability, efficiency, and aesthetics that's hard to match with other window materials.

While they come with a higher initial investment, their exceptional lifespan, minimal maintenance requirements, and energy-saving properties often make them the smartest long-term choice for your home. 

Ready to explore if fiberglass windows are right for your home renovation? Check out our in-depth review of Infinity from Marvin fiberglass windows, perhaps the best line of fiberglass windows on the market.