Why Fibrex Makes for Better Windows

 In Window Replacement

Most people have a good enough understanding of the advantages of energy-efficient windows. And with everyone from the Department of Energy to green building advocates and local Madison contractors promoting their use, it’s easy to see why more and more homeowners are investing in them.

Energy-efficient windows lower utility bills, lengthen the service life of heating and cooling equipment, and increase comfort inside homes and workplaces.

But what many homeowners fail to understand is that not all energy-efficient windows are created equal. Different components and mechanisms contribute to a window’s performance,
resulting in different levels of energy efficiency.


Window frames, for instance, tend to be points of heat and cold conduction, which means the choice of frame material will affect both solar and non-solar heat gain coefficients (SHGC and U- factor, respectively). Some of the most popular window frame materials—vinyl, wood, and aluminum—do not perform very well in terms of heat transfer. And no matter how low a window’s center-of-glass SHGC and U-factor are, a poor choice of frame material will have a detrimental effect on its overall efficiency.

The good news is that Renewal by Andersen offers a revolutionary composite framing material that takes care of this issue, and more. It’s called Fibrex.

Why Fibrex Makes for Better Windows

Fibrex is a family of composite materials that combines vinyl’s low maintenance requirement with the strength and stability of wood. Renewal by Andersen calls it both revolutionary and evolutionary, because it follows on the heels of their earlier forays into energy-efficient window frame research and development. They pioneered the manufacture of hollow vinyl windows in 1959 and went into engineered composite frames in the 60s and 70s. Having perfected composite window technology, Andersen began production of Fibrex windows in 1992.

Fibrex is made from a blend of re-claimed wood fibers and thermoplastic polymers in a weight-to-weight ratio of 40:60. The material is then extruded or injection molded into different
functional components that can be welded or mechanically fastened into products for specialized applications.

After production, all Fibrex products are then tested in simulated environments such as hot and cold chambers to measure their performance in extreme temperatures.

A product like Fibrex may perform well under carefully controlled laboratory conditions, but the real test of its durability comes upon installation. How well does it hold up to real-world
conditions? To answer that, let’s take a look at its primary physical properties.

Fibrex, being a family of composite materials, offers one huge advantage that window frames made of only a single primary material cannot match: it can be custom-engineered to suit a range of
customer requirements. Its main physical characteristics include:

  • Low thermal expansion coefficient – Thermal expansion is a measure of how much a material changes in volume after being subjected to a change in temperature. Fibrex has a thermal expansion coefficient of 1.6, while vinyl’s is 4.0. This means that Fibrex frames can go through extreme weather changes without undergoing as much warping, bowing, and cracking over time as vinyl.
  • Low thermal conductivity ratio – Fibrex’s insulating capacity is comparable to that of wood (pine) and vinyl and 700 times better than that of aluminum. This makes it capable of providing outstanding protection against heat transfer through windows.
  • High moisture resistance – The cell structure of the wood fibers in Fibrex is completely surrounded and filled with polymers. This makes the material resistant to moisture penetration and fungal growth, which means less rotting, peeling, and splitting over time—a huge advantage over both treated and untreated wood frames.
  • High flexural and tensile modulus – Fibrex is twice as rigid as vinyl, which makes it stiffer and more stable. Wood has a higher average modulus; however, unlike Fibrex, it has physical
    inconsistencies (like knots and grains) that make it less manageable. Fibrex therefore offers the best of both: strength and flexibility in form.

Why Fibrex Is the Best Window Frame Material

Renewal by Andersen believes in the extension, preservation, and protection of resources during the manufacturing process. Fibrex demonstrates this belief and makes it possible for homeowners to enjoy products that are environmentally friendly in more ways than one.

  • Renewing Existing Housing
  • Long Product Life Cycles
  • Smart Use of Energy of Materials

Here are some interesting facts about Renewal by Andersen Fibrex:

In 2008, Renewal by Andersen was recognized by Scientific Certification Systems (SCS) for their use of recycled materials. In Fibrex, they achieved the highest SCS-certified recycled content of any window replacement company: 40% reclaimed wood, 60% thermoplastic polymer. The thermoplastic polymer is itself recycled from other manufacturing processes. Even better, the Andersen recycles already-made Fibrex composites (from products not sold or sent out) to make more Fibrex.

Fibrex does not need wood preservative treatments or paint, which means that it doesn’t contribute to volatile organic compound (VOC) emissions. Using Fibrex helped Renewal by Andersen
earn the Indoor Advantage Gold certification from SCS. It is the country’s strictest indoor air emission standard, and Andersen is the only window company to date to have earned it.

Fibrex also helps homeowners reduce their carbon footprint in more ways than one:

Energy efficiency – Fibrex helps reduce energy consumption in living and work spaces by virtue of its thermal performance. The Department of Energy says that as much as 30% of energy consumed in each household is lost through windows, so every little bit helps.

Longevity – Fibrex windows do not need to be replaced as frequently as vinyl or wood windows. With the US already generating 124 million tons of debris from building demolitions alone each year, the less waste households and businesses send to landfills, the better.


When in need of high-quality windows or sliding patio doors for your home, just turn to Waunakee Remodeling and Renewal by Andersen of Madison. We’ll set up a meeting so we can help you explore your options and design the window or door unit that best suits your needs. Call us today at (608) 268-7140, or fill out this contact form to set up your window evaluation. We proudly serve all of south central Wisconsin, including areas in and around Madison.

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