Recycling Fiberglass Insulation Into Commercial Board Products

Gordon H. Hart

Gordon H. Hart, P.E., is a consulting engineer for Artek Engineering, LLC. He has over 35 years of experience working in the thermal insulation industry. He is an active member of ASTM committees, including Committees C16 on thermal insulation and F25 on marine technology, ASHRAE's Technical Committee on Insulation for Mechanical Systems, and the National Insulation Association's Technical Information Committee. He received his BSE degree from Princeton University. and his MSE degree from Purdue University, both in mechanical engineering. He is a registered professional engineer. He can be reached at gordon.hart®

July 1, 2001

For years, manufacturers and fabricators of fiberglass insulation have looked for cost-effective means of recycling fiberglass insulation. A major insulation contractor has evaluated and adopted an existing technology that can convert the stream of discarded glass fibers, generated as a by-product of fiberglass insulation manufacturing and fabrication, into saleable acoustical and thermal insulation board products. This contractor has recently designed and constructed a full-scale production facility to do this in Morristown, Indiana.

The technology starts with clean, dry industrial fiberglass insulation material. Then, the fiberglass is formed into a wet pack, resinated, dried, and cured into boards that have a density range from about 3 ½ to 7 lb/ft3, a thickness from 1 to 4 inches, and finished widths of up to 60 inches. The process is a unique recycling process whereby otherwise discarded glass fibers are made into commercially valuable board products.


A unique fiberglass recycling facility has recently been designed, constructed, and started in Morristown, Indiana. For the input fiber, this plant takes fiber from a major fiberglass manufacturer. This fiber is the trim and other discarded fibers that are the normal by-products of its manufacturing and fabrication processes and would otherwise be sent to a local landfill. The new recycling plant will convert this input fiber directly into commercially valuable, quality board products, without first melting that input fiber.

The particular recycling process is based on proven technology that has been modified and enhanced. A small, 160 lbs. per hour pilot line has been operated in Newark, Ohio since 1992; it converts discarded fiberglass insulation into excellent fiberglass boards. While the pilot line is limited to producing boards with a 24-inch width, they have superior compressive strength; also, they have thermal and acoustical performance comparable to other fiberglass boards of the same density, thickness, and fiber diameter. Most of this plant’s capacity is sold, primarily as acoustical treatment for building interiors.

The new production plant in Indiana uses a Fourdrinier-type wet process, adds an organic binder (a resin) solution, and then passes the wet, resinated fiberglass pack through a gas fired, high velocity convection curing oven. The process is unique for this application; the pilot line and the new production line are the only plants in the world making a fiberglass insulation board product from discarded fiberglass insulation without first remelting those fibers. Because no materials are melted, this is a low temperature, low energy consuming process. The only added ingredient is binder that makes up less than 10 percent by weight of the final board product. In addition, most dry trim or unused fiberglass material generated in the process is simply added back at the beginning of the line. Overall, this process generates very little waste; all liquid binder and water used are recirculated for reuse and most off-quality boards are simply reprocessed. This fiberglass conversion process has eight years of environmentally successful operation on a pilot line basis.

This new process lends itself to making custom products. The manufacturing line can be started up to make a specific amount of one product. The entire line can then be simply shut down, quickly adjusted, and then restarted making a different product. The change over takes a fraction of the time required for traditional processes and the small amount of ‘transition’ material is simply recycled. No melting furnace needs to be controlled and no molten material is used or wasted. This allows the plant personnel to change products several times a day and even to make custom orders, thereby reducing the need for large product inventories.

Description of the Original Pilot Line Plant

The pilot line has been operating since 1992 and is located in Newark, Ohio. This basic manufacturing process combines new adaptations of the proven Fourdrinier forming process that is used in the paper and fiber mat manufacturing industries with an innovative oven curing process based on those used in fiberglass insulation manufacturing.

Input fiber is first received as either compressed bales or loose material, which is processed into a uniform condition. The processed, dry input fiber is then mixed with water to form slurry. The prepared slurry is pumped to the Fourdrinier type forming box at the desired production rate for the factory. The forming box consists of an inclined, moving mesh, forming conveyor that collects the fiberglass fibers as the water drains through the conveyor, converting the slurry to a wet fiberglass pack. Almost all of the water is recycled with the addition of make-up water for slurry preparation.

After most of the water has been extracted by vacuum, binder is applied to the fiber pack by flooding with a thermo-setting phenolic resin binder solution. The excess binder solution is then extracted from the fiber pack with the use of suction fans, further reducing moisture content. The extracted binder solution is returned to the binder application process. After binder extraction and prior to entering the curing oven, the wet fiber pack enters a dryer where moisture content is reduced to about 60 percent.

After the dryer, the moist pack enters the curing oven. The curing oven has upper and lower moving screens, with side seals, and natural gas burners with a large fan. Perforations in the screens allow heated air to be forced through the fiberglass pack by means of the circulating fans. The heated air first evaporates the water and then cures the binder. The top screen can be raised or lowered to set the thickness of the product. The oven has different zones where airflow is reversed (top to bottom, bottom to top), and air temperature is controlled for proper curing. After curing, the binder locks the fibers together giving the finished product its thickness, density, and physical and chemical properties.

Some of the oven exhaust gases are used to preheat the combustion air and some of the other oven exhaust gases are used as make-up air for the de-watering and binder extraction areas. These warm exhaust gases help to remove some moisture from the fiber pack and the wet fiber pack partially scrubs the exhaust gases of volatiles that otherwise would go out the exhaust stack.

When the product leaves the oven, it is trimmed to width and sheared to length. Depending on the requirements of the finished product it can also be bisected, sanded and/or faced prior to packaging. Most edge trim, saw or sanding dust and off-ware are returned to the process as input fiber. There is very little waste generated.

Description of the New Plant

The new production line has a far greater capacity than the pilot line. The following is a description of the technical operation of the recycling operation for the production facility:

Production Line Raw Fiber Handling

Clean, dry raw input fiber is received from fiberglass manufacturers and fabricators and sorted and segregated according to fiber category. Workers remove facings and any interleaving material; they cut larger boards into smaller pieces; and balance the input of the fiber by categories required for a particular blend of finished board.

Raw fiber is hand loaded onto conveyors in each of two sorting areas. The fiber is fed through a metal detector and onto a chopper machine. The choppers are individually set for each category of fiber. Figure 1 shows input fiber being loaded onto a conveyor.

Chopped fiber flows onto a conveyor, and when the pre-measured batch volume has been reached, the conveyors stop until the next batch cycle starts. The different categories of fiber combine and are then carried by conveyor to batch mix tanks.

Production Line Slurry Batch Mixing

Batch volumes are based on the desired production throughput. A concentrated fiberglass – water slurry is created as the mix tank fills. Batch sizes can vary depending on the concentration required for the product being made.

The concentrated slurry is further homogenized and then pumped into a slurry supply tank. During this process, it is diluted with White Water that is recycled from the discharge of the downstream production. If the forming section requires more or less fiber, the concentrated slurry flow rate is changed accordingly. Figure 2 shows the various conveyors and tanks used in the slurry batch process. Figure 3 shows the fiberglass – water slurry in a mix tank.

Production Line Former and Dewatering Sections

The Former and Dewatering equipment, employing a modified Fourdrinier process, is designed for the capacity of the plant at a fixed slurry feed rate. The production width can be set at a minimum of 51 inches (nominal 4 foot) and a maximum of 63 inches (nominal 5 foot). Production thickness can be set between 1 and 4 inches. The speed of the line can be changed to maintain a fixed solids output with different widths, thickness and density.

A large percentage of the water is mechanically removed from the pack by a high velocity vacuum prior to thermal drying. This "White Water" from the former section is subsequently separated from the air by moisture separators and is recirculated.

Production Line Binder Storage and Mixing

Binder is made up in batches prior to use. Chemical additives are then supplied by a small metering pump to adjust pH and help to increase the binder solubility. When the binder is ready for use, it is pumped to a "Binder Ready Tank". Binder is continuously supplied to the pack and the excess is collected and recirculated.

Production Line Dryer

Figure 5 shows the wet pack as it enters the multi-zone dryer conveyor/oven, expressly designed to evaporate water but not to cure the binder. Some of the dryer exhaust air is ducted to the binder and White Water dewatering sections. This heated air is pulled through the wet fiber pack where most of the volatile organic compound gases (VOCs) are absorbed by the water in the wet fiber pack and then are exhausted to the outside of the building. Some of this air is reheated and recycled through the dryer. Figure 6 shows this production line dryer.

Production Line Curing Oven

The curing oven is a unique multi-zone conveyor/oven designed specifically for this plant. The oven not only supplies and maintains the correct flow rate and air temperature required for the range of products, but also supplies/recycles the exhaust to the dryer and forming sections at temperature and rates that maintain an efficient energy and mass balance for the entire process.

Fiberglass board products then leave the curing oven hot and with no moisture.

Production Line Post-manufacturing

After emerging from the curing oven, the boards undergo the following post manufacturing processing. This includes convective cooling, side trimming, cutting to length, bisecting, and surface sanding.

Dust Collection

A dust collector is located in the material handling area. It is used to collect edge trim, bisect saw waste and sanding waste.

Reuse of Waste Materials Generated

Much of the fiberglass material that is trimmed, sanded, or otherwise removed during production and all off-quality products are simply reprocessed. There is little scrap generated by the process. Also, there is no liquid waste with the new plant, because all water used in the wet process is recirculated and the liquid binder solution is recycled. Because of this new plant, the flow of discarded fiberglass and combustible packaging materials otherwise going to landfill should be substantially reduced and converted into commercial products.

Properties of the Fiberglass Boards Produced by the Process

This process of making fiberglass boards from recycled fiberglass insulation is unique. Mineral fiber insulations are typically manufactured by melting raw input material (such as rock, slag, sand, or recycled glass) and forming hot fibers that are sprayed with binder, air-cooled, and then formed into an uncured pack. The uncured pack is then passed through a curing oven, which compresses the pack to its final thickness and cures the binder.

By contrast, this new recycling facility uses a wet process, starting with glass that has already been fiberized, adding water to make slurry and then using a modified Fourdrinier forming box to create a thick, wet pack. The wet pack is then resinated, dried and cured.

Because the fibers are already formed and cooled, and water, instead of air, is used to form the pack, the boards have both similar and unique characteristics. In general, those similarities and differences are discussed below:

Control Over Product Density and Thickness

Once a mass production rate has been selected, density and thickness are simply controlled by a combination of the line speed and thickness setting on the curing oven. The process has been used to continuously manufacture boards with densities between 3 ½ and 7 lb/ft3 and thicknesses between 1 and 4 inches.

Control Over Manufactured Product Width

With typical air formed mineral fiber products, a particular manufacturing machine is limited to one width. If there is a need for a finished product with a narrower width, it can only be made by trimming a cured board. By contrast, the process can form and cure a pack at different widths by simply adjusting the width of the Fourdrinier forming box, and resetting guards on the water and fiber extraction, the dryer, the curing oven, and the trim saws.

Control Over the Distribution and Amount of Added Binder

Binder is added as a solution flowing over a weir onto the wet pack. Varying the solution’s concentration is used to control the quantity of added binder. And, because the entire pack is saturated by binder solution, all areas of the pack receive a uniform binder coating.

Control Over Surface Quality

Because the boards are made from shorter, randomly oriented fibers, they can be readily sanded to give exceedingly smooth surfaces. The consistency of these surfaces is only limited by the accuracy of the sanding equipment; this new plant’s equipment has consistently made surfaces with +/- 1/32-inch finished thickness. Also, because this surface is consistent and smooth, it can be effectively painted with light paint coatings as well as faced with less adhesive.

Compressive Strength

Boards made by the process have significantly higher compressive strength values, for a given density, than is typically found for air formed fiberglass boards. For example, a 6 lb/ft3 density board has a tested compressive strength, at 10 percent deformation, of about 600 lb/ft2, per ASTM C165, Method A.

Fiber Diameter

With an air formed mineral fiber product, fiber diameter is set by the spinner hole size used to make the fibers and cannot be changed without great difficulty and expense. In fact, it is typically held constant for a given machine. The mean fiber diameter of the boards is based on the mean fiber diameter of the input fibers, so adjusting the fiber mix can change it. On the pilot line, discarded fine fiber building and pipe insulation has been successfully used to produce boards with a mean fiber diameter in a range from 20 to 35 hundred thousandths of an inch (HT).

Flame Spread

Both 4 and 7 lb/ft3 boards have been tested for flame spread and been shown to have a Class A fire rating.

Thermal Conductivity

As with other mineral fiber insulation products, the thermal conductivity of a board, for a given mean temperature, depends on bulk fiber density and mean fiber diameter. Tested values for thermal conductivity are comparable to those for other commercially available fiberglass board products of the same density and fiber diameter.

Sound Absorption

Sound absorption, for a given thickness and frequency, depends primarily on thickness, bulk fiber density, and mean fiber diameter. The board sound absorption values are comparable to those for commercially available fiberglass boards of the same thickness, bulk fiber density, and mean fiber diameter. For example, 2 inch thick, 7 lb/ft3 density boards made with 28 HT diameter fibers have a tested Noise Reduction Coefficient equal to 1.05.

Product Customization

A major advantage of the process over typical air formed mineral fiber manufacturing processes is ease of transitioning from one product to another (i.e. changing thickness and density) and the fact that the process works with inventoried raw fiber. This allows for plant staff to custom manufacture products and not have to rely strictly on inventoried products. Because the line can be started up or shut down with the push of a button, it is far easier, with this process, to change between one product and another.

ASTM C612 Compliance

Based on the performance tests conducted, fiberglass boards manufactured by the process meet the requirements of ASTM C612, Type 1B.


A unique wet process pilot line has operated for eight years, successfully manufacturing fiberglass boards from discarded fiberglass material. This new facility takes large quantities of clean, dry fiberglass, which would be otherwise discarded and sent to landfill, and converts it into high quality fiberglass board products.

The boards made by this process are similar to mineral fiber insulation boards made by the traditional air formed process. Thermal and acoustical properties are comparable, for a given thickness, bulk fiber density, and mean fiber diameter. However, the process also creates some unusual product characteristics. Compressive strength is greater and the product possesses the ability to be finished to a finer thickness tolerance. While the total binder content may be higher than traditional boards (due to the resident binder that is present on some of the input fiber), the binder distribution is extremely uniform. This gives these boards a more consistent appearance and performance.

This process has the potential to significantly reduce the quantities of discarded mineral fiber insulation currently going into landfills by converting this discarded material into high quality board products. As such, it represents an exciting new recycling technology for trim and off-quality mineral fiber insulation materials that otherwise would be discarded.