Are Andersen Fibrex Windows Better Than Vinyl Windows?

Open Casement Windows on House 482184921
Open Casement Windows on House. Getty / Fotosearch

Vinyl (polyvinylchloride or PVC) is the material most often used to make cheap, effective windows.  Yet industry leader Andersen's core lines of windows are largely vinyl-averse.

Instead, it favors the use of a proprietary material called Fibrex for its windows.  Is Fibrex a better material for your windows, as Andersen says?  

Fibrex Basics 

Fibrex is Andersen's patented (#5,486,553) composite material that it uses for a majority of its windows as a structural member.  

By weight, Fibrex is composed of 40% recycled Ponderosa pine wood fibers and 60% polyvinylchloride (PVC, or vinyl).

It was initially developed to lower Andersen's costs by reusing sawdust obtained from the production of its wood windows.  

One concern of exposed wood is rot.  However, since each of Fibrex's wood fibers is surrounded and coated with PVC, it cannot rot since it has no exposure to the elements

Series That Use Fibrex

  • 100 Series
  • A-Series
  • Renewal by Andersen

Andersen does use majority PVC in some of its windows, but these windows are not part of Andersen's core business.  

Instead, it prefers to confine vinyl to three separate business units:  Silverline (a company purchased solely to help Andersen gain a foothold in the vinyl realm); Craftsman (do-it-yourself windows found on Home Depot shelves); and Renewal by Andersen (its replacement window unit).

Is Fibrex Really Better Than Vinyl?  

Andersen's marketing literature is technically honest about Fibrex.  However, this information is ambitiously presented and gives a would-be purchaser the impression that Fibrex is vastly superior to vinyl.  This is not the case.

1.  Insulating Properties

For example, Andersen says that "Fibrex material has superior thermal insulating properties" in comparison to aluminum window frames, which "conduct heat and cold."  

Independently, both statements are true.  However, aluminum against Fibrex is not an apt comparison.  Most window shoppers considering Fibrex are looking in the vinyl/fiberglass/Fibrex area, not aluminum.  

More importantly, at a thermal conductivity rating of over 0.60, aluminum is the single most thermally conductive material that Andersen's marketing department could have chosen to compare to Fibrex (about 0.15).

A better comparison to Fibrex is vinyl.  Internal sell sheets provided to Andersen salespeople even state that Fibrex's "insulating properties can be put on par with pine or vinyl" (Fibrex: Engineered For Performance, 2007)

2.  Sagging and Bowing

One problem with vinyl windows, especially darker color vinyl, is sagging, bowing, and other deflection when subjected to high heat. 

Andersen states that Fibrex stands up better against heat distortion than vinyl.  Again, this is true--but only barely.

Fibrex's heat distortion threshold is 173 F, compared to vinyl's threshold of 163 F.  So, even though Fibrex's threshold is ten degrees higher than that of vinyl, both materials remain below the distortion starting point of 180 F.

How Fibrex Benefits You

  • Lower Thermal Expansion:  Because pine has a low thermal expansion rate, these fibers help to control Fibrex's overall expansion rate.  As such, vinyl expands at more than twice the rate (4.0) vs. Fibrex's rate (1.6).
  • Greater Compressive Strength Than Vinyl:  Andersen's claim that Fibrex is twice as strong as vinyl is true, but only in terms of compressive strength.  The benefit to you is not so much that you get a stronger window but that the window frame is slimmer, resulting in more glazing.  More glazing means more light.

How Fibrex Benefits Andersen

  • Wood As Cheap Filler:  Wood is cheaper than vinyl, especially when that wood is recycled from another operation.  It is no mistake that Fibrex's patent application refers to the wood as "filler."  Fibrex benefits Andersen because the company uses byproducts of its wood window production for all of the wood fiber used in Fibrex; in essence, it gets free materials.  Some vinyl is recycled from the production of Andersen vinyl cladding, too.  But since Andersen produces so few vinyl clad windows, it needs to supplement with virgin vinyl.  
  • Extruded or Injection-Molded:  In developing Fibrex, Andersen wanted a fiberglass-like product that could be extruded (extruding means to push a soft material through a shaping filter) or injection molded.  Fiberglass cannot be extruded or injection-molded, resulting in simpler lines and shapes.
  • Sold To Other Companies:  Through marketing company Aspen Research, Andersen sells Fibrex as a general purpose wood composite that can be used for purposes unrelated to windows.

    How Fibrex Benefits Everyone

    While Andersen's development of Fibrex was out of self-interest, it was a self-interest that benefits the environment.  

    Any end product that uses waste products can be considered eco-friendly.  Andersen's reuse of wood fibers is especially beneficial because not all of this is clean wood dust.  Much of it contains adhesives, paint, primer, anti-fungal agents, and a host of other contaminants.  

    So, keeping the wood dust out of landfills or incinerators means keeping these contaminants out of the earth and atmosphere.