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 (aka insulation fiberglass) plays an important role in reducing energy use and carbon dioxide emissions. The material is also used in duct 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.

Because borates absorb infrared radiation, their incorporation into building products such as polymers, plastics, coatings, and other materials helps prevent heat loss through infrared transmission. Yet, they also serve an additional purpose, aside from improving our homes’ efficiency. Borates’ fire-retardant properties help 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—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 (ie, dissolve in the lung if inhaled during installation) and resistant to water and chemicals.

Borates in insulation work as a protector

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 plastics and elastomers

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 as flame retardants for polymers. Although its applications are extensive and varied, Firebrake ZB, for example, is a multipurpose synergist in both halogen-containing and halogen-free polyolefin. 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 boron based fire retardant applications are numerous:

  • 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 (ie, 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?
  • Less product caking
  • Granulometry compatiblity with other glass batch components
  • Consistent and reliable quality: Customers can use our certificate of authenticity (COA) data in batch formulation, eliminating the need for onsite QA/QC and improving the production process
  • Decades of research and expertise: Exclusive, extensive knowledge regarding boron volatility, borate chemical and physical analysis and troubleshooting, and global regulations

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


These products are unique zinc borates combining the best of zinc and boron oxides that can be used to develop fire-retardant formulations. Learn More


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

More About Borates in Insulation and Polymers 

Firebrake ZB: A Modern Choice for Fire Retardancy in Polymers
Fire safety is not just about preventing fire, but ensuring that if a fire happens, people can escape it. 20 Mule Team® Borax Firebra... Learn More
Borates Are the Multi-Tool for Fire Safety in Plastics and Polymers
Borates provide a multifunctional approach to promoting fire retardancy in the polymers and plastics that are prevalent in today’s homes and business co... Learn More
Borates Power Up Energy Efficiency Efforts
From increasing home efficiency to maintaining sustainable policies at our own facilities, U.S. Borax and the borates we produce help reduce energy use and co... 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 northeast of Los Angeles.  Learn more about Rio Tinto.

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