Fiberglass Replacement Windows from Infinity® by Marvin®

Looking for long-lasting, energy-efficient replacement windows in Colorado? Fiberglass windows from Infinity® by Marvin® are built to outperform vinyl and maintain their performance for decades without warping, cracking, or fading.

At Gravina's Window Center of Littleton®, we’ve been replacing windows in Colorado homes since 1973. As Colorado’s oldest Infinity® by Marvin® dealer and one of the longest-tenured in the nation, we understand what performs in this climate and what fails over time.

Infinity® windows are built with patented Ultrex® pultruded fiberglass, engineered for extreme temperature swings, high UV exposure, hail, and dry conditions. Unlike vinyl, fiberglass remains stable over time, helping maintain a tight seal, consistent energy performance, and long-term durability.

For homeowners who want the look of real wood, the EverWood® interior option can be stained or painted to match your home without the maintenance of traditional wood. Every Infinity® window is backed by an industry-leading limited lifetime warranty for long-term protection.

When you choose Gravina's Window Center of Littleton®, you’re working with a family-owned company that has installed Infinity® by Marvin® windows in more than 15,000 Colorado homes. No national chains, no shortcuts, and no handoffs. Just window replacement done right.

Window and Door Replacement with Infinity® by Marvin®

Home projects can feel overwhelming, but replacing your windows does not have to be. At Gravina's Window Center of Littleton®, we manage every step from your first consultation through design, delivery, and professional installation, so you always know what is happening and what comes next.

Fiberglass does not warp, crack, or swell the way vinyl or wood can. That matters in Denver, where temperature swings of 50 degrees in a single day are common, and UV exposure at altitude accelerates material breakdown faster than most window manufacturers account for. Infinity® by Marvin® fiberglass windows are built specifically for those conditions, and our installation teams have handled them in more than 15,000 Denver metro homes.

Over our 50+ years in business, we have completed projects of every size, from single-room window updates to full-home transformations. When you choose Gravina's Window Center of Littleton®, you get access to the complete line of Infinity® by Marvin® fiberglass windows and doors, sized and customized to fit your home exactly.

Infinity® by Marvin® Fiberglass Window Styles for Colorado Homes

Awning windows are hinged at the top and open outward diagonally. This design offers maximum airflow and allows rain to slide off when opened during storms.
Bay windows: These windows have three panels set at 30- to 45-degree angles that protrude from your home. They offer architectural interest and create additional interior space for seating or storage.
Bow windows: Similar to bay windows, these form a 3D shape but have a more curved angle.
Casement windows: These windows attach by one or more hinges on the side and open to the left or right.
Double-hung windows: These windows have a movable upper and lower sash for maximum ventilation and easy cleaning.
Round top windows: These fixed windows come in a half-moon shape and add decorative touches to any room.
Single-hung windows: This style has a movable lower sash and fixed upper sash for added security, especially in ground-floor rooms.
Single-hung round-top windows add a quarter or half-moon arch to typical sing-hung windows.
Slider windows: Also known as glider windows, these move along a track to the left or the right and work best in rooms with limited space.
Unique shape windows: These decorative fixed windows come in various shapes, including pentagons, trapezoids, and octagons.

Infinity also offers in-swing French doors, sliding French doors, sliding patio doors, and bi-fold doors.

Are Fiberglass Windows Better Than Vinyl in Colorado?

In Colorado’s climate, fiberglass windows consistently outperform vinyl. At the core of every Infinity® by Marvin® window is Ultrex® pultruded fiberglass, a material engineered for strength, stability, and long-term performance.

Ultrex® fiberglass is eight times stronger than vinyl, expands and contracts at nearly the same rate as glass, and does not absorb moisture. This helps maintain a tight seal over time, reducing drafts, seal failure, and long-term wear. For Colorado homeowners dealing with freeze-thaw cycles, high UV exposure, and extreme temperature swings, that is not a marketing claim. It is an engineering advantage.

Infinity® by Marvin® also offers advanced energy-efficient glass options, including Low E2, Low E3, and LoE3-366 coatings. These options reduce heat transfer, improve comfort, and help lower energy costs without sacrificing natural light. Our team helps you select the right glass package based on your home’s orientation, exposure, and performance goals.

Why Installation Matters as Much as the Window

Even the best window will underperform if it is not installed correctly. At Gravina's Window Center of Littleton®, most projects involve full-frame replacement. This means removing the entire window, frame, and trim to ensure a precise fit, improved insulation, and long-term durability.

Our team handles the entire process from start to finish, including measurement, installation, and finishing. Custom painting and staining ensure your new fiberglass windows integrate seamlessly with your home. No subcontractors, no handoffs, and no shortcuts.

Why Fiberglass Outperforms Vinyl in Colorado Homes

Infinity® by Marvin® fiberglass windows are built with patented Ultrex® fiberglass, engineered to handle Colorado’s extreme temperature swings without warping, sagging, or cracking. Vinyl expands and contracts at a rate significantly higher than glass, which can break down seals, distort frames, and reduce energy performance over time.

Many of the vinyl windows we replace in Denver metro homes are less than ten years old. Fiberglass expands and contracts at nearly the same rate as glass, helping seals stay intact, frames stay stable, and performance last for decades. Choosing fiberglass means investing once instead of replacing windows prematurely.

Energy Savings with Infinity® by Marvin® Fiberglass Windows

Energy-efficient windows can reduce heating and cooling costs by 11% to 37%.* Infinity® by Marvin® fiberglass windows combine advanced glass packages with strong, insulated Ultrex® frames to deliver consistent performance in Colorado’s climate.

At higher elevations, standard Low-E coatings do not always perform the same as they do at sea level. Our team helps homeowners select the right glass package based on home orientation, sun exposure, and heating needs, so the performance you expect is the performance you experience.

Why Homeowners Choose Gravina's Window Center of Littleton®

With more than 53 years of experience and over 15,000 installations across the Denver metro area, Gravina's Window Center of Littleton® is Colorado’s most experienced source for Infinity® by Marvin® fiberglass replacement windows and doors. As a family-owned company, we focus on proper installation, long-term performance, and a level of service that national chains and private equity-owned window dealers cannot match.

Schedule your free consultation or visit our Littleton showroom to see Infinity® by Marvin® fiberglass windows in person. Colorado homeowners have trusted us since 1973 for window replacement done right.

Frequently Asked Questions About Fiberglass Windows

What makes fiberglass windows a better choice than vinyl for Colorado homes?

Ultrex® pultruded fiberglass is 8 times stronger than vinyl and 3 times stronger than Fibrex®, making it the strongest window framing material in the replacement industry. That strength matters in Colorado, where temperature swings of 50 degrees in a single day are common and UV exposure at altitude accelerates material breakdown faster than at sea level. Vinyl also expands and contracts at roughly 7 to 8 times the rate of glass, breaking down seals and distorting frames, often within the first decade. Fiberglass moves at nearly the same rate as glass, so seals stay intact and frames stay true for decades. At Gravina's Window Center of Littleton®, many of the windows we replace in Denver metro homes are vinyl windows less than ten years old.

How long do Infinity® by Marvin® fiberglass windows last?

Infinity® by Marvin® fiberglass windows are backed by an industry-leading limited lifetime warranty and are engineered to outlast the home improvement cycle entirely. Ultrex® pultruded fiberglass does not rot, corrode, absorb moisture, or fade under UV exposure. In Colorado's climate, properly installed fiberglass windows routinely perform for 30 to 40 years or more without structural degradation.

What is Ultrex® fiberglass and why does it matter?

Ultrex® is a patented pultruded fiberglass material developed by Marvin. It is eight times stronger than vinyl, does not absorb moisture, and expands and contracts at nearly the same rate as the glass it holds. The same pultrusion process used to manufacture Ultrex® is used in aerospace and industrial applications. For Denver homeowners, that means a window frame that holds its shape, maintains its seal, and delivers consistent energy performance through decades of Colorado freeze-thaw cycles and high-altitude UV exposure.

Are Infinity® by Marvin® fiberglass windows energy efficient in Colorado's climate?

Yes, and the glass package matters as much as the frame. Infinity® by Marvin® offers several advanced glass options including Low E2, Low E3, and the exclusive LoE3-366/ERS coating. At Colorado's altitude, standard Low-E coatings do not always perform as rated at sea level. Gravina's Window Center of Littleton® helps Denver homeowners select the right glass package for their specific home orientation, sun exposure, and heating zone, so the energy savings are real, not just rated. Independent studies show energy-efficient windows can reduce heating and cooling costs by 11% to 37%.*

Who is Colorado's oldest Infinity® by Marvin® dealer?

Gravina's Window Center of Littleton® has been an authorized Infinity® by Marvin® dealer since 2003, making us Colorado's oldest and one of the three longest-tenured Infinity® dealers in the nation. Since 1973, we have served Denver metro homeowners from our Littleton showroom and have installed Infinity® by Marvin® fiberglass windows in more than 15,000 homes across the Denver metro area.

What is the difference between full-frame replacement and insert window replacement?

An insert replacement fits a new window inside the existing frame opening without removing the surrounding trim or siding. A full-frame replacement removes the entire window assembly, frame, trim, and all, down to the rough opening. Most projects completed by Gravina's Window Center of Littleton® involve full-frame replacement because it delivers a precision fit, better insulation at the rough opening, and a completely updated appearance inside and out. Our team assesses each opening individually and recommends the approach that delivers the best long-term performance for your specific home.

Can I see Infinity® by Marvin® fiberglass windows before I buy?

Yes. Gravina's Window Center of Littleton® maintains a full working showroom at 209 W Littleton Blvd in Littleton, Colorado, where you can see and operate Infinity® by Marvin® fiberglass windows and doors in person. Our team is available Monday through Friday, 8 am to 5 pm, and Saturday, 9 am to 3 pm. Schedule a free consultation or stop in at your convenience.

Last Updated: March 20, 2026

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