Andersen Fibrex Windows vs. Vinyl Windows Comparison

After the reign of aluminum windows in the 1960s, it was thought that vinyl windows (polyvinylchloride or PVC) would be the next best thing, forever. Plastics brought the promise of windows that never had to be maintained: no scraping, no painting. And while vinyl is still a hugely popular material for making cheap, effective windows, one industry leader, Andersen Windows, reduces its use of vinyl. Instead, Andersen favors the use of a proprietary composite called Fibrex. Since Fibrex is a price-point competitor with vinyl, how do the two materials compare in consumer-level replacement and new-construction windows?

What Are Fibrex Windows? 

Fibrex is Andersen's patented PVC-wood composite material that it uses for a majority of its windows as a structural member. By weight, Fibrex is composed of 40-percent recycled Ponderosa pine wood fibers and 60-percent polyvinylchloride. Fibrex 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 rots at a far slower rate than pure wood.

In developing Fibrex, Andersen sought 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.

Fibrex is found in Andersen's 100 Series, A-Series, and Renewal by Andersen lines. Andersen has been slowly exiting the majority-PVC window market for years. At one time, Andersen owned Silverline, which Andersen purchased solely to gain a foothold in the vinyl window market; that was sold in 2018. Andersen also owned the do-it-yourself vinyl replacement window company American Craftsman, found at Home Depot. Andersen divested itself from American Craftsman in 2018 in the same sale to Ply Gem. Renewal by Andersen remains as Andersen's only replacement window unit.

Fibrex vs. Vinyl Windows Comparison

Insulating Properties

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. Aluminum against Fibrex may not be a valuable comparison, though, since window shoppers considering Fibrex are usually looking at vinyl or even fiberglass windows, not aluminum. 

More importantly, at a thermal conductivity rating of over 0.60, aluminum is a highly thermally conductive material (compared to Fibrex, which has a rating of about 0.15). A more accurate 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."

Heat Distortion Point

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. Fibrex's heat distortion threshold is 173 F, compared to vinyl's threshold of 163 F. So, even though Fibrex's threshold is 10 degrees higher than that of vinyl, both materials remain below the distortion starting point of 180 F.

Thermal Expansion

Because pine has a low thermal expansion rate, these wood fibers help to control Fibrex's overall expansion rate. As such, vinyl expands at more than twice the rate (4.0) compared to Fibrex's rate (1.6).

Compressive Strength

Andersen's claim that Fibrex is twice as strong as vinyl is true, but only in terms of compressive strength. The benefit is not so much that you get a stronger window but that the window frame is slimmer, resulting in more glazing. More glazing brings more light into your home.

Green Benefits

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, Andersen gets free materials out of the deal. 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. 

While Andersen's development of Fibrex benefits the company, it also 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.