Boron in Insulation and Polymers


When it comes to keeping our homes and workplaces comfortable and energy-efficient, we often turn to cellulose or glass wool insulation. Used for thermal and acoustic insulation of residential and commercial buildings, glass wool (also called insulation fiberglass) plays an important role in reducing energy use and carbon dioxide emissions. The material is also used induct and pipe wrap for refrigeration, heating, ventilation, and air conditioning systems. Whether in the form of blankets (rolls), batts (precut slabs), or loose fill (blowing wool), glass wool represents the largest single use of borates worldwide.

And, because borates absorb infrared radiation, their incorporation into building products such as polymers, plastics, coatings, and other materials helps to prevent heat loss through infrared transmission. Yet they also serve an additional purpose, aside from improving our homes’ efficiency. Borates’ fire-retardant properties help to keep insulation and polymers—and thus the buildings they are used in—safe.

Glass wool insulation

Glass wool works by trapping air within its mesh of fibers, thus reducing the rate of heat transfer. The most important role of borates in these glass fibers is to increase absorbance of infrared radiation, which significantly increases the insulation performance of the roll, batt, or wool.

In glass wool manufacturing, borates also act as a powerful flux, lowering glass batch-melting temperatures. They also control the relationship between temperature, melt viscosity, and surface tension, creating optimal glass fiberization. The result is short, strong fibers that are biosoluble (i.e., dissolve in the lung if inhaled during installation) and resistant to water and chemicals.

 Borate Insulation

Boric oxide (B2O3) enables minimization of the fiberizing temperature of glass wool, while maintaining aqueous durability. Otherwise, atmospheric moisture could attack and weaken the fibers during storage under compression and prevent the insulation batt from recovering to its correct thickness. The presence of boric oxide is essential in maintaining the product's insulation value. It also increases the infrared absorption of the fibers, improving the insulation value and reducing of the product’s density.

Fire-retardant polymers, plastics, and PVCs

Specialized borate compounds, such as zinc borates, are used as fire retardants and smoke suppressant additives in polymers, plastics, and rubber applications. 

20 Mule Team® Borax Firebrake® products, Firebrake 500 and Firebrake ZB, are designed for polymer protection. Although its applications are extensive and varied, Firebrake ZB, for example, is a multipurpose synergist in both halogen-containing and halogen-free polyolefin. There, it acts not only as a flame retardant and anti-arcing agent, but as a smoke and after glow suppressor and a promotor of char formation. As a fire-retardant synergist, the product completely or partially replaces antimony oxide in the final product. The applications for such capabilities are numerous:

Polymer flammability

  • Wire and cable products
  • Electrical connectors and bobbins
  • Circuit breakers and housings
  • Transformer components
  • Appliance components
  • Wall coverings
  • Foam insulation
  • Mechanical parts
  • Conveyor belts
  • Carpet backing
  • Automotive upholstery
  • Roofing membranes
Char: A hard, intumescent (i.e., expanded) residue that some polymers produce during combustion. In effect, part of the polymer is transformed into a solid, carbonaceous mass rather than into smoke or flame. Char reduces the duration of a fire, inhibits its spread, provides electrical insulation to protect wiring even after it is burnt, and prevents short-circuiting and sparking.

Why 20 Mule Team Borax?

Why use 20 Mule Team Borax products instead of antimony oxide or competing borates for fire suppression in insulations and polymer products and production?
  • 20 Mule Team Borax products experience less caking.
  • Our products are granulometry compatible with other glass batch components.
  • Our product quality is consistent and reliable. Customers can use our certificate of authenticity (COA) data in batch formulation, eliminating the need for onsite QA/QC and improving the production process.
  • We have exclusive, extensive knowledge regarding boron volatility, borate chemical and physical analysis and troubleshooting, and global regulations, thanks to decades of research and expertise.

20 Mule Team Borax Products

These 20 Mule Team Borax products are developed for use in the manufacture of insulation and polymers.

Ammonium Pentaborate

Whether inhibiting heat, flame, or corrosion, the purity of this alkaline salt makes it an excellent choice. Learn More


This hard, glassy, granular product is excellent when forming flux or glass, where it helps to increase yield and reduce energy consumption. Learn More

Firebrake 500

As a dehydrated zinc borate, Firebrake 500 has numerous applications as a fire retardant and can be fed into extruders, calendars, and injection molding equipment. Learn More

Firebrake ZB

This unique zinc borate combines the best of zinc and boron oxides with water release. Use it to develop fire-retardant formulations processable up to 290°C. Learn More


With lower transportation, handling, and storage costs, this concentrated sodium borate is used in glass and fiberglass, cleaning products, flame retardants, and more. Learn More


From reducing melting temperatures in fiberglass production to inhibiting corrosion in fuel additives, Optibor has a multitude of uses in numerous industries. Learn More

Borates in Insulation and Polymers 

Boric Oxide for Insulation Fiberglass
Boric oxide is widely used in fiberglass formulations because it has remarkable and relevant glass-forming, fluxing, and viscosity-lowering properties. Learn ... Learn More
Long-Life Straw and Other Benefits of Borates
Borates offer significant benefits across numerous global industries, enabling safe, effective, innovative uses of sustainable materials. Learn More

U.S. Borax, part of Rio Tinto, is a global leader in the supply and science of borates—naturally-occurring minerals containing boron and other elements. We are 1,000 people serving 500 customers with more than 1,700 delivery locations globally. We supply 30% of the world’s need for refined borates from our world-class mine in Boron, California, about 100 miles east of Los Angeles.  Learn more about Rio Tinto

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