What Is Fibrex? Andersen's Composite Window Material Explained

If you've been researching Andersen windows, you've seen "Fibrex" mentioned repeatedly. It's Andersen's proprietary composite material and a key differentiator from both vinyl and wood windows. Here's what it actually is.

What Fibrex Is Made Of

Fibrex is a composite material made from a blend of reclaimed wood fiber (from Andersen's own manufacturing process) and thermoplastic polymer (PVC). The wood fibers provide structural strength and rigidity while the polymer provides moisture resistance and dimensional stability. The result is a material that's approximately twice as strong as vinyl but doesn't rot, flake, or blister like wood.

How Fibrex Performs vs Vinyl vs Wood

• Strength: Fibrex is roughly 2x stronger than vinyl, allowing for narrower frame profiles (more glass, more view) without sacrificing structural integrity
• Thermal expansion: Fibrex expands and contracts significantly less than vinyl in temperature extremes — important in Illinois where temperatures range 100+ degrees between summer and winter
• Moisture resistance: Unlike wood, Fibrex doesn't absorb moisture, so it won't rot, warp, or swell
• Paintability: Fibrex can be factory-painted in a range of colors with a durable finish that holds up to UV and weather
• Environmental: Made with 40% reclaimed wood fiber that would otherwise be waste from Andersen's manufacturing

Which Andersen Windows Use Fibrex?

The Andersen 100 Series is the primary Fibrex product line — it's Andersen's most affordable option and uses Fibrex for both the interior and exterior frame. Renewal by Andersen (a separate company) also uses Fibrex exclusively. The Andersen 200, 400, E-Series, and A-Series use different materials (wood, Perma-Shield, aluminum-clad, and fiberglass). Full Andersen product line review →