Combatting Combustion: Borates in Cellulose Insulation

:: Tuesday, April 18, 2023 :: Posted By Emmanuel Laval

For decades, we’ve trusted cellulose insulation in our attics, walls, and even ceilings to maintain comfortable indoor temperatures and lower energy costs.

Cellulose insulation is one of the safest and most reliable building materials available today. But what you may not realize is that it’s also one of the most federally regulated products due to its combustion propensity.

Because borates combat both smoldering and flame combustion, they are widely used in cellulose insulation to meet regulations and fire safety standards.

Despite their prevalence, you may still have questions about borates such as:

  • Which borate product is right for my process?
  • What’s the right concentration to meet fire safety standards?
  • Why does it matter who I partner with for my borate needs?

Answering these questions will help you produce effective products, overcome regulatory hurdles, and avoid any costly warranty claims in the future.

Why do we use borates in cellulose insulation?

A primary reason is that borates improve cellulose insulation’s central function: Reducing heat loss.

However, it was borates’ ability to resist flame and smolder that led to widespread adoption.

In the 1970s, as expensive energy bills rocked households across the globe, people turned to cellulose insulation to quickly improve their home’s heating efficiency and relieve pressure on their wallets.

Cellulose insulation became popular because it’s:

  • Affordable
  • Widely available
  • Easy to install
  • An effective heat insulator and sound barrier
  • Made from environmentally friendly materials
  • It is fire, mold and insect resistant

As cellulose insulation’s popularity exploded, the U.S. government became increasingly concerned with product safety. That led to an order from the Consumer Product Safety Commission outlining performance standards for cellulose insulation in fire conditions.

Other organizations followed suit, such as the American Society for Testing and Materials (ASTM), which developed a comprehensive cellulose insulation testing standard, ASTM C379.

To meet this standard, cellulose insulation is commonly treated with boric acid (or other borates), which serves as both a flame and smoldering retardant.

Borate-based treatments are economically viable and provide long-lasting benefits. Structures using borate-treated cellulose insulation are better equipped to resist combustion and slow the spread of fire.

Considerations for borate-treated cellulose insulation

Selecting the right product and ensuring the proper concentration of borates for your cellulose insulation can be tricky.

To make this process easier, U.S. Borax offers a number of products for cellulose insulation manufacturing. Our three most popular products in the industry are:

Most cellulose insulation producers use Optibor, a high-quality boric acid product that can stand alone in your insulation’s fire-retardant formulation. Optibor is extremely effective at suppressing smoldering combustion, ensuring you’ll meet necessary safety standards.

If you’re looking for a borate that excels at suppressing flame combustion and resists corrosion, look no further than Neobor. By combining Neobor with Optibor, you can also take advantage of Optibor’s outstanding ability to stand up to smoldering combustion.

If you’re treating cellulose insulation with a liquid solution, Polybor is an excellent choice. Like our borate products above, Polybor equips cellulose insulation with flame and smoldering combustion resistance, while also deterring corrosion.

It's important to determine the correct loading of borates in your cellulose insulation treatment. Depending on the product, the recommended borate treatment level falls between 10-20%.

All batches of U.S. Borax products adhere to tight particle size thresholds and high standards, resulting in more consistent and dependable loading.

Success is more than choosing the right product

For more than 50 years, we’ve been a trusted partner of cellulose insulation producers. If you contact our technical team, we can help you:

  • Achieve high fire safety ratings
  • Meet critical industry standards such as ASTM C739
  • Navigate evolving regulations
  • Ensure your products have the right borate concentration
  • Reach your sustainability goals

We’re excited to be closely involved with the industry as an associate member of the Cellulose Insulation Manufacturers Association (CIMA). If you’re at CIMA’s annual meeting, we’d love to answer any questions you may have about your cellulose insulation needs.




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 650 customers with more than 1,800 delivery locations globally. We supply around 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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