When shopping for new windows, you may hear a lot about fiberglass — and for good reason. Fiberglass windows are known for their strength, energy efficiency, and long-lasting performance, especially in climates like Wisconsin where weather can fluctuate dramatically. But what actually goes into making fiberglass windows?
At Windows of Wisconsin, we proudly install Infinity from Marvin windows made with Ultrex® fiberglass, and we want to give you a simple, homeowner-friendly look at how this impressive material is created — and why it matters for your home.
Why Homeowners Choose Fiberglass Windows
Before diving into the manufacturing process, here’s why fiberglass is such a popular choice:
- Durability That Lasts: Fiberglass won’t warp, crack, rot, or swell the way wood or vinyl can. It’s designed to withstand Wisconsin’s freezing winters, humid summers, and temperature swings.
- Excellent Energy Efficiency: Fiberglass insulates better than aluminum and has much lower expansion and contraction than vinyl. This helps keep your home comfortable and reduces strain on your HVAC system.
- Low Maintenance: No painting. No peeling. No warping. Just long-lasting performance with simple cleaning.
- Modern, Attractive Style: Fiberglass allows for slim frames, clean lines, and a variety of shapes and colors — perfect for both traditional and modern homes.
How Fiberglass Windows Are Made
Fiberglass windows have a more advanced manufacturing process than vinyl or aluminum, and this is what gives them superior performance. Here’s a high-level look at how they’re created:
Step 1: Creating Fiberglass Strands
Fiberglass begins as a combination of natural materials — mostly silica sand and other minerals — melted down into liquid form. This molten glass is then pulled through tiny openings to create extremely thin, strong glass fibers.
These fibers are the foundation of fiberglass windows.
Step 2: Forming Strong Window Frames
Once the fibers are created, they’re combined with a high-strength resin (think of it like a bonding glue). This mixture is then pulled through a heated mold that shapes the frame pieces. This process is called pultrusion — and it’s what gives Ultrex fiberglass its unmatched strength and stability. The result?
Window frames that are:
- Consistently straight
- Incredibly strong
- Highly resistant to expanding or contracting
This stability is one of the biggest reasons Infinity from Marvin uses Ultrex exclusively.
Step 3: Assembling the Window
Once the fiberglass frame components are formed:
- They’re cut to size
- Joined together to create the window frame and sash
- Fitted with high-performance glass
- Sealed for airtight performance
- Finished with durable acrylic coatings
- Completed with top-tier hardware and weatherstripping
The finished product is a window that’s built to last — and built to perform in tough climates like Wisconsin.
Why This Matters for Wisconsin Homes
Fiberglass isn’t just strong — it’s stable. That makes a huge difference in states with weather swings like ours.
1. Minimal Expansion and Contraction: Ultrex expands at nearly the same rate as glass. Vinyl expands up to 8x more.
Less movement means:
- No seal failures
- No drafts
- No fogging between panes
- Less air leakage
- Longer window life
2. Better Insulation
Fiberglass conducts very little heat, helping keep warm air inside in winter and outside in summer — reducing heating and cooling costs.
3. Long-Term Durability: Wisconsin weather is tough.
Ultrex stands up to:
- Freeze-thaw cycles
- High winds
- Heat and humidity
- UV exposure
This makes fiberglass one of the best-performing materials for Midwest homes.
How to Choose the Right Fiberglass Windows
When selecting fiberglass windows, focus on:
✔ Energy Efficiency: Look for Low-E glass, gas fills, and ENERGY STAR® ratings.
✔ Frame Strength: Not all fiberglass is made the same — Ultrex is the strongest on the market.
✔ Aesthetic Options: Choose styles that fit your home (casement, double-hung, picture, etc.).
✔ Professional Installation: Proper installation is crucial for long-term performance and efficiency.
At Windows of Wisconsin, we combine industry-leading Infinity from Marvin windows with expert installation to ensure your home gets windows built to last.
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Ready to Learn More About Fiberglass Windows?
If you’re considering upgrading your windows, our team can walk you through the process, explain what sets Ultrex fiberglass apart, and help you choose the right style for your home.
We proudly serve homeowners throughout Green Bay, Appleton, Oshkosh, Neenah, Freedom, and nearby communities.
📞 Call (920) 429-9119 to schedule your free consultation today.
Your home deserves windows built to perform — and we’re here to help.
