My wife and I are looking at Sunrise replacement windows. They seem to be very sturdy windows with a nice lifetime warranty. I've heard that I definitely want to get some kind of structurally reinforced vinyl window as vinyl by itself is not very strong. In looking at how these windows are reinforced, the best I've come up with is this statement:

FiberCore Plus, a pultruded fiberglass I-beam reinforcement that is coupled with urethane insulation comes with every door to add to the strength of the design.

(from here)

How does Fiberglass compare to aluminum/steel reinforcement structurally? Is fiberglass reinforcement sufficient/superior/worse? Should I be concerned with fiberglass reinforcement in any way? How will the reinforcement material impact the window's lifespan?

Note, I'm in the Mid Atlantic (Maryland).

  • It's going to depend (to a large degree I would have thought) on the climate. Where are you?
    – ChrisF
    Commented Sep 7, 2010 at 18:08
  • @ChrisF just updated the question with that info. Thanks.
    – Doug T.
    Commented Sep 7, 2010 at 18:14
  • 1
    I don't know how they compare specifically, but one consideration -- fiberglass can't be welded, so it may be strong over its length, but weak at the corners where it's connected. (this assumes the 'I beams' are formed in advance, then cut to fit; it'd be possible to custom make them as one piece, but much more difficult, and thus, expensive .)
    – Joe
    Commented Sep 7, 2010 at 18:36

2 Answers 2


I live in MN and we recently replaced all of our windows with replacement inserts (Marvin Windows). After talking with several experts (and 4 different companies) they all agree wood is still the best. The issue with Vinyl is/was the brittleness in colder climates. Fiberglass is supposed to help with that but it is relatively new so there is no long-term analysis that can be done. In summary: Fiberglass is supposed to be good but is unproven.


Reinforcement is very important for vinyl windows. That said, lower quality vinyl windows always need reinforcement to help with warping. This only minimizes or delays warping due to the low quality. These include all the vinyl windows sold at Home Depot, Lowe's, and other building supply stores. Although not all those are reinforced. High quality vinyl windows won't warp but are reinforced to minimize deflection which is when strong winds hit a window causing the window to bow ever so slightly and allow air to infiltrate. This happens to wood windows, aluminum and vinyl. Reinforcement also allow the window hardware to be fastened to both vinyl and reinforcement. Fiber glass and other composite materials are used as reinforcement because they are not thermally conductive like aluminum and steel.

High quality vinyl window brands are Okna, Gorell, Polaris Ultra series, Soft lite, and sunrise. All of these windows are reinforced. However, I don't think the Sunrise window hardware is fastened to the fiberglass.

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