What Is Fiberglass and How Is It Manufactured?

Making, using, and recycling this durable, lightweight material

Home renovations showing with rolls of insulation
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Fiberglass, or “glass fiber,” much like Kleenex, Thermos—or even Dumpster—is a trademarked name that has become so familiar that people usually only think of one thing when they hear it: Kleenex is a tissue; a Dumpster is an oversized trash bin, and Fiberglass is that fluffy, pink insulation that lines the attic of your house, right? Actually, that’s only a part of the story. While the Owens Corning Company did trademark the near-ubiquitous insulation product known as Fiberglass, fiberglass itself has a familiar base structure and a wide variety of uses.

How Fiberglass is Made

Fiberglass really is made of glass similar to that in windows or kitchen drinking glasses. To manufacture fiberglass, glass is heated until molten, then forced through superfine holes. This creates glass filaments that are extremely thin—so thin, in fact, that they're best measured in microns.

These flexible filament threads can be used in several applications: They can be woven into larger swatches of material or left in a somewhat less structured form used for the more familiar puffy texture used for insulation or soundproofing. The final application is dependent on the length of the extruded strands (longer or shorter) and the quality of the fiberglass. For some applications, it's important that the glass fibers have fewer impurities, however, this involves additional steps in the manufacturing process.

Manufacturing With Fiberglass

Once the fiberglass is woven together, different resins may be added to give the product increased strength, as well as allow it to be molded into various shapes. Common items made of fiberglass include swimming pools and spas, doors, surfboards, sporting equipment, boat hulls, and a wide array of exterior automobile parts. Having a light yet durable nature, fiberglass is also ideal for more delicate applications, such as in circuit boards.

Fiberglass can be mass-produced in mats or sheets. For instance, for items such as shingles, a massive sheet of a fiberglass and resin compound is manufactured and then cut by machine. Fiberglass also has numerous custom-made applications designed to suit a specific purpose. For example, car bumpers and fenders must sometimes be custom-made, either to replace damaged components for existing automobiles or in the production of new prototype models.

The first step in manufacturing a custom-made fiberglass bumper or fender is creating a form in the desired shape out of foam or some other material. When the form is complete, it's coated with a layer of fiberglass resin. Once the fiberglass hardens, it's subsequently reinforced—either with additional layers of fiberglass or structurally from within.

Carbon Fiber and Glass-Reinforced Plastic vs. Fiberglass

It should be noted that although it's similar to both, fiberglass is not carbon fiber, nor is it glass-reinforced plastic. Carbon fiber is made of strands of carbon. Though extremely strong and durable, carbon fiber cannot be extruded into strands as long as those of fiberglass because it breaks. This is one of several reasons that fiberglass, while it's not as strong, is cheaper to manufacture than carbon fiber.

Glass-reinforced plastic is just what it sounds like: plastic with fiberglass embedded in it to increase strength. The similarities to fiberglass are apparent, but a defining characteristic of fiberglass is that the glass strands are the main component. Glass-reinforced plastic is comprised mostly of plastic, so while it's an improvement over plastic alone for strength and durability, it won't hold up as well as fiberglass.

Recycling Fiberglass

Although there hadn't been much advancement in the recycling of fiberglass items once they'd already been produced, some new innovations in recycling technology and uses for recycled fiberglass products are starting to emerge. One of the most promising is the recycling of outdated wind-turbine blades.

According to Amy Kover, a reporter for GE Reports, General Electric’s in-house news site, while replacing existing blades with more technically advanced ones can increase wind farm performance by as much as 25%, the process creates the inevitable waste. “Crushing a blade yields about 15,000 pounds of fiberglass waste, and the process creates hazardous dust. Given their enormous length, sending them to a landfill whole is out of the question,” she noted.

In 2017, GE teamed up for a recycling initiative with a Seattle-area-based Global Fiberglass Solutions Incorporated (a company that’s been recycling fiberglass since 2008, and has patented a means to recycle old blades into products including manhole covers, building panels, and pallets). In less than a year, GFSI recycled 564 blades for GE and estimated that in the coming years, GE would be able to re-manufacture or reuse up to 50 million pounds of fiberglass waste.

In addition, a great deal of fiberglass itself is currently manufactured from recycled glass. According to the National Waste and Recycling Association's newsletter "Waste360", recyclers are turning broken glass into a viable resource known as cullet (glass that's been crushed and cleaned), which in turn, is being sold to manufacturers of fiberglass insulation. "Owens Corning uses more than one billion pounds of cullet every year for residential, commercial and industrial fiberglass applications," they report. Meanwhile, Owens Corning has stated that as much as 70% of their fiberglass insulation is now manufactured using recycled glass.


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Johnson, Todd. "What Is Fiberglass and How Is It Manufactured?" ThoughtCo, Sep. 8, 2021, thoughtco.com/what-is-fiberglass-or-glass-fiber-820469. Johnson, Todd. (2021, September 8). What Is Fiberglass and How Is It Manufactured? Retrieved from https://www.thoughtco.com/what-is-fiberglass-or-glass-fiber-820469 Johnson, Todd. "What Is Fiberglass and How Is It Manufactured?" ThoughtCo. https://www.thoughtco.com/what-is-fiberglass-or-glass-fiber-820469 (accessed May 30, 2023).