We’re here to help you find the best fiberglass windows on the market today. These are our top picks that receive solid reviews from both consumers and industry insiders. Fiberglass windows are going to be stronger and slightly better looking than vinyl, but they tend to run 30% to 40% more than vinyl. Compare fiberglass vs vinyl windows.
Bottom Line: There are differing opinions on who makes the best fiberglass windows – therefore don’t hesitate to use the links to read consumer reviews on each of our picks.
(Always collect 3 to 4 additional bids)
Bill — Site Editor
Best Fiberglass Windows | Alpen 925
The Alpen 925 series is perhaps the best fiber glass replacement window on the market today. In fact, the whole line up from Alpen is pretty impressive. The 925 series attains a 9.1 R-value, which is a very impressive energy efficient rating. The Alpen 925 window can be order as a casement, fixed frame, awning, bay window, bow window, or as a sliding patio door. The real downside is availability – contact Alpen Windows to find out if there is a dealer who services your zip code.
Target Price Point: $2400 fully installed
Inline Fiberglass Windows
While not well known to the public, Inline Windows of Ontario Canada makes a really nice fiberglass window. Like many of their competitors, the Inline products incorporate a thin profile to their base model (which consumers can customize using ala carte pricing for each desired upgrade.)
Standard features include 100% pultruded fiberglass frame, Cardinal glass, optional metal components, and a fiberglass wind screen. These windows should be available through local window distributors in much of the northeast. However, because Inline is based in Canada, their reach is relatively limited more many American consumers looking for the best fiberglass windows on the market.
Target Price Point: $2600 fully installed
Marvin Essential Collection
The Marvin Essential Collection is our first pick. The Essential is an all fiber glass series with a modern and clean look. The Essential is a re-imagined Marvin Integrity (see below) and can be ordered in a retrofit or as a new construction window (which includes a nailing fin). The Essentials Collection will be expensive, but that’s to be expected with Marvin.
Target Price Point: $2200 fully installed
Fiberglass Windows Cost
Fiberglass windows cost will run anywhere from $1200 to $2600 fully installed. This is a big price range, and actually doesn’t take into account what fiber glass bids might come in at. We hear of Marvin Windows cost bids coming in at $2K plus per “unit” fully installed all the time.
As a rule of thumb, fiberglass window costs will run 30% to 35% more than vinyl windows. It’s one of the reasons why it tends to be out of the price range of many Americans. Check out our Harvey windows prices page to see how much vinyl windows cost compared to fiber glass.
Marvin Elevate Series
The Marvin Elevate Collection is the company’s new take on the Marvin Integrity series with the Ultrex wood on the interior. The Elevate uses a fiberglass exterior cladding and a pinewood on the interior. This is a very nice looking and expensive option. The Elevate collection can be ordered as a retrofit or as a new construction window (which includes a nailing fin). All in all, one of the best fiberglass windows on the market and one of my favorites.
Target Price Point: $2500 fully installed
Marvin Integrity Series
The Marvin Integrity series is no longer listed on the company’s website. It is, however, still available through certain dealers. The Marvin Integrity fiberglass window is available in two profiles; the Wood Ultrex or the All Ultrex. The Wood Ultrex windows have fiberglass exteriors and wood interiors.
The All Ultrex have the fiberglass on both the exterior and the interior. This window is available in the following styles; Awning, Casement, Bay, Bow, Double Hung, Slider, Round Top, Polygon, Sliding French Door, Inswing and Outswing French Door and Sliding Patio Door. The one knock on the Integrity is that it is very limited in sizes and options.
Target Price Point: $1800 fully installed
Best Fiberglass Windows: Marvin Infinity
The Marvin Infinity series is no longer listed on the company’s website. However, the window is still available through certain dealers. This Infinity looks great and the workmanship on these fiberglass windows is top-of-the-line. They look almost as good as wood, with the great strength of fiberglass, high energy efficiency and they are almost maintenance free.
Additionally, the Infinity is only available in fiberglass, tends to be more expensive than the Integrity, and is available in more options and colors. One of the best fiberglass windows on the market for sure.
Target Price Point: $1900 fully installed
Milgard Ultra Series
The Milgard Ultra Window is available as either a replacement or as a new construction window. The frame is constructed from fiberglass, but is intended to look as close to a wood window as possible. The Ultra DH was pulled from the market to fix design flaws and was off the market for 3 years.
There were issues with the compression jambs (water and air could pass through), paint finish, poor screens, etc. However, the company fixed these problems and the window is fairly well regarded by some but not all industry insiders. Milgard offer a good warranty, but unfortunately their customers tend to need it more often than Marvin for instance.
Target Price Point: $1750 fully installed
Pella Impervia Series
Despite what many consumers think, the Pella Impervia window is possibly one of the worst fiberglass series out there. (My opinion, not everyones.) I find it flimsy and unattractive. On the plus side, it can be easily customized and many people do like the frame profile. The real reason most people think it is so good is the name Pella. My take on them is this: they make a very nice wood clad series in the Designer and Architect. Beyond this, I think there are better options available.
Like many Pella products, the Impervia often carries a hefty price tag. Additionally, the window is available as a double hung and casement – consumers seem to like the casement over the double hung. Despite the high cost, the performance numbers on the Pella Impervia window are not overly impressive.
Target Price Point: $2300 fully installed
Best Fiberglass Windows Quotes
Scroll down to explore consumer price quotes and project bids on the top fiberglass window options on the market. However, do remember that these are bids and not what the homeowners eventually paid. Additionally, bids and quotes are often more expensive than what the consumer ends up paying if they are smart enough to know how to negotiate with window salesman.
Inline Casements
24 Casements And 2 Patio Doors
e.g. Price Point: $68K
Also Included All Installation
Location: Upstate New York
Project Quote from 2025
Milgard Ultra Pricing
6 Double Hung Windows
e.g. Price Point: $9.6K
Also Included All Installation
Location: Los Angeles, California
Project Quote from 2024
Marvin Infinity Windows Cost
4 Fixed Windows, Plus 1 Awning
Sizing: Variable
e.g. Bid Pricing: $6.7K
Also Included All Costs
Place: Seattle, Washington
Project Quote from 2019
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Window Replacement Cost
Pella Windows Reviews
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