Best Fiberglass Windows

We’re here to help you find the best fiberglass windows for your home. Here are our top picks that receive solid reviews from consumers and industry insiders. Of course, there are always differing opinions on fiberglass window manufacturers – that’s why we have provided links to replacement window reviews for each of these selections so homeowners can judge independently on the pros and cons of these so-called best fiberglass replacement windows.

“Homeowners looking for the best fiberglass replacement windows should expect to pay $80 to $2000 per window fully installed…and yes, this is a big price range!”

Quality Replacement Window Companies

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.

Best Fiberglass Windows | Marvin Integrity

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.

Window Brand Quality
Installation Requirements
How Many Windows?
Zip Code

Fiberglass Windows Cost

Fiberglass windows cost will run anywhere from $900 to $1800 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.

Best Fiberglass Windows | Marvin Elevate

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).

Best Fiberglass Windows | Marvin Integrity

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 availalble 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.

Best Fiberglass Windows | Marvin Infinity

The Marvin Infinity series is no longer listed on the company’s website. It is, however, still available through certain dealers. This window 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. The Infinity is only available in fiberglass, tends to be more expensive than the Integrity, and is available in more options and colors.

Marvin Infinity Windows Cost

4 Fixed Windows, Plus 1 Awning
Sizing: Variable
Bid Pricing: $6.7K
Included Everything
Place: Seattle, Washington
Project Quote from 2019

Quality Replacement Window Companies

Best Fiberglass Windows | Milgard Ultra

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. They 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.

Pella Impervia

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. It 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.

Related Topics

Fiberglass Windows
Window Replacement Cost
Pella Windows Reviews