Best Fiberglass Replacement Windows



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Best Fiberglass Windows 2023

We've put together six of the best fiberglass windows currently available. Find product descriptions, contractor opinions and pricing, which ranges from $1100 to $2000 fully installed. There are other quality options, but these are our selections for the best fiberglass windows.

Tom - HWRC Editor - Page Updated In December, 2023



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Alpen 925 Series

Alpen 925 fiberglass windows are the company's top of the line model and delivers up to a 9.1 R-value and 99.5% UV protection. It is one of the top rated series on the market and also one of the most expensive. The window can be ordered as a casement, awning, fixed frame, half circle, bow or bay, and sliding patio door. It includes all of the grid and SDL options, as well as the paint and finish options of the 525 and 725 series. The casement window with the Alpine glass 9L will deliver a .15 U factor, 6.7 R-value, .22 SHGC and a .34 VT. These are some pretty fantastic numbers, but obviously it does come at a price.

Price Range: $1600 to $1900 installed


Marvin Infinity Series

Marvin Infinity fiberglass windows has an Ultrex fiberglass frame that comes as either a full Ultrex or as an exterior Ultrex with an Everwood interior (this is a wood veneer that looks very similar to wood, without any of the maintenance). The Infinity is a replacement window, although it is probably available as a full frame replacement given some customization. The Infinity is more expensive than the Integrity and has a thicker frame, some better "bells and whistles", a better finish to the frame and a better warranty (lifetime on everything except the glass, which is 20 years). The performance numbers on the Infinity are good (but not great); U-factor of 0.30. The Infinity is the better window and if you can afford it and don't have to have wood, this is a good quality window.

Price Range: $1400 to $1800 fully installed


Inline Fiberglass Series

Inline fiberglass windows are one of the lesser known but higher end window manufacturers that is headquartered in Canada. Their products are not cheap, but are well made and designed. Their products have a thin profile to maximize glass area, use Cardinal glass, quality paint ,100% pultruded fiberglass frames, and a high quality screen. Inline is priced out using the stripped down window as the base price - every upgrade you add to it - glass, fills, screens, hardware, warranty adds to the base price for a per unit final price. The company gets knocked for some outdated hardware and limitations on sizes and dimensions.

Price Range: $1600 to $2000 installed


Milgard Ultra Series

Milgard Ultra fiberglass windows are often considered a second choice behind the Infinity or Integrity. The Ultra lacks the the fantastic look of the Infinity Everwood, which is their wood veneer interior. One positive of the Ultra is areal wood interior option (just as the Integrity is available in the wood interior). The company offers a nice warranty on their products. If the Marvin products are out of your price range and you are married to fiberglass, the Milgard is a decent choice.

Price Range: $900 to $1200 fully installed



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Marvin Integrity Series

Marvin Integrity fiberglass windows are the slightly lower end fiberglass frame that comes as either a full Ultrex or an exterior Ultrex with a real wood interior. There are far fewer options available in the Intgrity, both in terms of sizing, colors, hardware etc. While it is a nice looking window, most industry insiders feel it's not as nice as the Infinity (and has less of the bells and whistles of the Infinity). It should come standard with a Cardinal glass package (20 year warranty on glass), has a lifetime warranty on the frame and 10 years on defects. A good option for homeowners who want a wood interior with a fiberglass exterior at a reasonable cost.

Price Range: $1300 to $1600 installed


Pella Impervia Series

Pella Impervia fiberglass windows have a clean, thin profile and is available in custom sizing (although some contractors are put off by both the fit and finish of this window). It is available as a double hung and casement - some customer didn't like the look of the double hung. The Pella has less than stellar performance numbers (U-value of 0.33) which is not particularly impressive. It uses a mid range metallic spacer and is priced somewhat high based on comparable offerings.

Price Range: $1400 to $1600 fully installed







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Best Fiberglass Windows 2022


Marvin Fiberglass Infinity Series

7 Double Hungs
Sizes: Normal Sized
Bid Price: $10.7k
Included All
Location: Northeast Wisconsin
Year: 2022


Best Fiberglass Windows 2021


Serious 525 series

6 Double Hungs
Dimension: 36" by 60"
Quote: $1455 per window
Included All Project Aspects
Location: New York
Bid From 2021

Inline 900 series

6 Double Hungs
Dimension: 36" by 60"
Quote: $1414 per window
Included All Project Aspects
Location: New York
Bid From 2021

Fibertec 400 series

6 Double Hungs
Dimension: 36" by 60"
Quote: $1350 per window
Included All Project Aspects
Location: New York
Bid From 2021






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