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three windows for testing andersen fibrex pella impervia fiberglass

Pella Fiberglass vs. Andersen Fibrex

It's a One-Sided Fight – Spoiler Alert: Pella Wins

See how our exclusive fiberglass material outperforms Andersen Fibrex plastic/wood composite to hold up better for the strength and durability your home or project demands.

Won't Bend
Pella fiberglass is on average

stronger than Fibrex in a bend test.72

Won't Dent
Pella fiberglass is on average

more impact resistant than Fibrex.59

Won't Break
Pella fiberglass is on average

the tensile strength of Fibrex.73

Compare the Superior Strength of Pella Fiberglass vs. Andersen Fibrex

As much as the competition in a bend test, which measures the flexural strength of a material by applying force via a single, concentrated load point in the middle.


3-point bend testing performance based on testing 10 samples of each material using ASTM D790 test methodology.

Pella® Impervia® – 100% Fiberglass. 0% Wood Fiber.

Take a look behind the paint and see what materials make up Pella's proprietary fiberglass and Andersen Fibrex.

a close view of pella's fiberglass material

Pella Impervia, made of our proprietary fiberglass

Our fiberglass starts with our structural mat which places rovings in a specific, intricate order to meet Pella’s high strength standards. The mat and additional rovings are pulled through a machine, injected with polymer resin and heated to create an entirely new, thermoset material. Our fiberglass material is the strongest available for windows and patio doors.61

andersen's fibrex material failed the hammer test

Andersen Fibrex, made of plastic, wood fiber and glue

Contrary to popular belief, Andersen Fibrex is not fiberglass, but is instead made of 40% wood fibers and 60% plastic that is fused together with glue to create the window or door frame. Without strong fiberglass rovings and mats, this thermoplastic material used on Andersen 100 Series and Renewal by Andersen Fibrex products is susceptible to breaking and shattering.

Find the Right Product For Your Project

Work with a dedicated Pella representative every step of the way.

pella rep helping a window customer

See how we simulated a slipping hammer on a jobsite to see the damage.

Watch the Video


Testing our Fiberglass to the Extremes
Watch the Video


Pella Fiberglass vs. A Bowling Ball

To demonstrate how well our proprietary fiberglass material holds up to impact, we decided to take things to extremes and go far beyond our normal testing practices. We created a test where we dropped a 10-pound bowling ball onto a section of our fiberglass sliding patio door jamb lineal (the frame of your door) — from seven feet in the air.

More Extreme Tests
testing material by dropping a volleyball onto a piece of fiberglass material
Pella Fiberglass vs. A Bowling Ball
Now Playing
testing material hanging cinder blocks off a piece of fiberglass frame
Behind the Bend Test
testing material by hanging a pickup truck from a window frame
Strong enough to lift a heavy-duty truck
woman with white blouse using the easy slide operator on a casement window
Get the Best Fiberglass Windows & Patio Doors

Designed to stand up to everyday wear and tear, Pella Impervia products offer an on-trend color palette, including black, and feature our latest innovation, the Easy Slide Operator window hardware, winner of Best in Show at the 2021 International Builders Show.

Explore Additional Product Details

Ready to take the next step?

Work with a dedicated Pella representative every step of the way.


Pella products are backed by some of the strongest warranties in the business.

Learn more about Pella warranties