Boron in Insulation


When it comes to keeping our homes and workplaces comfortable and energy-efficient, we often turn to cellulose or glass wool (aka insulation fiberglass) insulation. Used for thermal and acoustic purposes in residential and commercial buildings, insulation 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. You can also find certain types of insulation in hard durable goods such as ovens, refrigerators, and dishwashers.

Whether in the form of blankets (rolls), batts (precut slabs), or loose fill (blowing), insulation represents the largest single use of borates worldwide.

Cellulose insulation

Cellulose insulation is used mainly as loose-fill for insulating lofts, attics or cavity walls, though spray-on varieties are available for application to ceilings or side walls by means of an adhesive. Because cellulose insulation is primarily made of wood, cotton, and other plant-derived raw materials, it is inherently flammable and prone to smoldering combustion.

The use of borates in cellulose materials imparts flame retardancy, enabling them to meet stringent safety standards and regulations. U.S. Borax Optibor® boric acid has long been recognized as an effective flame retardant additive due to its capability of preventing smoldering combustion. The combination of Optibor and Neobor® yields reliable fire and corrosion performance. Borates are soluble in water and can be sprayed as aqueous solution on the shredded paper during the manufacturing process. The high solubility and high boron content of Polybor® often make it a preferable choice for wet application.

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.

Why 20 Mule Team Borax?

Why use 20 Mule Team Borax products instead of antimony oxide or competing borates for fire suppression in insulation 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 insulation use.

Ammonium Pentaborate

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

U.S. Borax is an associate member of:


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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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