Boron in polymers: A proven flame retardant

Borates in polymer and coating formulations ensure safety, maintain integrity

Polymers are everywhere—from plastics and wiring to building materials and cars. Despite clear benefits, polymers ignite and burn easily—a trait manufacturers must try to inhibit by creating an effective fire-retardant formulation.

That’s why many polymer formulations incorporate zinc borates during processing. Compared to other flame-retardant additive choices available today, borates are naturally occurring, multi-functional, and possess strong synergistic effects when used with other flame retardants.

When you’re balancing factors such as cost, quality, process stability, and safety, even a small concentration of borates can improve your formulations without disrupting sensitive production processes. Borates can help polymers exceed flammability requirement standards such as UL94 and reach the market as safe, durable products. While boron’s use as a flame retardant is the primary commercial application in polymeric materials, borates can impart valuable benefits in coatings.

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Zinc borates: Effective fire retardant

For better performance against flame, smoke, and arcing, sourcing high-quality, refined borates is vital.

Zinc borates are versatile—you can add them to halogen-containing or halogen-free polymer formulations. Depending on formulation needs, you can use zinc borates independently or combine them with other flame retardants such as metal hydroxides aluminum trihydroxide (ATH) and magnesium dihydroxide (MDH).

Compared to market alternatives, our refined borates possess low impurity levels, consistent morphology, high thermal stability, and high bulk density. These attributes positively impact benefits such as:

  • Inhibiting flame combustion: When combustion conditions are present, borates can release water from their structure to inhibit flames.
  • Promoting char formation: When flames ignite, borates form a carbonaceous char and a vitreous, insulation-like layer that strengthens and stabilizes the char. Char slows pyrolysis and produces a barrier to impede the release of additional gases that can fuel combustion.
  • Suppressing smoke formation and afterglow: Borates’ ability to turn part of a polymer into char rather than smoke helps reduce harmful air for consumers.
  • Anti-tracking/anti-arcing agent: For materials producers who need to instill low electrical connectivity properties in their polymers, boron provides anti-tracking and anti-arcing benefits.
Almost any type of polymer system can benefit from borates’ fire retardant properties, including:
  • Coatings (acrylic, epoxy, polyurethane)
  • EPDM rubber
  • Epoxy
  • Neoprene
  • Phenolic
  • Polyamides (PA6, PA66, PA12)
  • Polycarbonate
  • Polyester
  • Polyolefins (polypropylene, polyethylene, EVA)
  • Polystyrene
  • Polyurethane
  • PVC
  • SBR
  • Silicone rubber
  • Unsaturated polyester
  • WPCs (HDPE/PP/PVC with natural fibers)

Zinc borates’ high thermal stability, synergistic qualities avoid process disruption

Any moisture in your incoming raw materials can disrupt your process, resulting in costly defects. Some fire-retardant additives start releasing water at 200°C, causing bubbles or blisters to appear. Firebrake® zinc borates possess high thermal stability—an important quality during extrusion, where high temperatures melt and shape polymers.

Ensuring cooperation between all additives in a formulation is equally important to successful processing. Borates are halogen-free and synergistic, enhancing other additives’ capabilities under certain conditions.

How coatings benefit from zinc borates

Many coating formulations feature borates as an additive, with zinc borate as one of the most used. While zinc borates are most known for fire retardant characteristics, they possess additional key benefits for a range of coating applications. 

  • Anti-corrosion: Both organic solvent-based and water-based coatings can benefit from the anti-corrosion properties zinc borates impart.

  • Infrared radiation (IR) absorption: Borates absorb IR radiation and reduce radiative heat transfer, making them great for applications such as greenhouse film covers using polyethylene or polycarbonate.  

  • Tannin stain blocking: Wood primers and topcoats treated with zinc borates can significantly reduce discoloration of wood coatings.

  • Ultraviolet (UV) protection: Zinc borates are made by synthesizing zinc oxide and boric acid. Zinc oxide works as an ultraviolet absorber in polymer materials, reducing harmful ray exposure and extending the life of the material.

  • Adhesion promotion: A coating’s durability rests on proper adhesion. Zinc borates can help adhesion between coating films and metal substrates.

  • Stability: Adding zinc borates to aqueous paint stabilizes the pH level, a crucial property that fights paint’s propensity to gel or coagulate.

Why work with U.S. Borax to make your polymers effective and fire retardant?

We offer high-quality products, a rich history of research and development, sustainability benefits, and technical expertise.


Elevated product quality

For 150 years, we’ve been a world leader in refined borates. Our reputation depends on mining and refining high-quality products that satisfy stringent specifications. Even the slightest impurities can have major negative consequences such as product discoloration, production equipment damage, and negative processing events such as burning—that’s why we ensure quality standards in every batch.

Research and development pioneers of zinc borates

More than 50 years ago, we brought zinc borates to market with Firebrake® ZB, a patented product with a proprietary molecular formula. We continue to expand technical resources to help you with your specific use cases for borates in polymer applications
People watch planes drop fire retardants on the LA fire in 1961.
Repurposed war planes (“Borate Bombers”) with borate compound helped fight enormous wildfires near Los Angeles in the 1960s.

Unparalleled technical expertise

Our technical team can equip you with knowledge to test and develop formulations that meet your specific polymers and coatings needs. Plus, we can recommend loading for formulations and provide other guidance so your polymers can meet your product requirements.
Learn more about which materials use borates, application methods, and formulation factors to consider. Get the brochure →

Achieve your sustainability goals

Consumer and regulatory stakeholders are more ESG conscious than ever. By partnering with U.S. Borax, you can assure them you are sourcing from a responsible, sustainable producer. We’re investing in projects to reduce our carbon footprint, improve land and resource stewardship, and increase diversity in operations

20 Mule Team Borax Products

Recommended for polymers and coatings

Borogard ZB logo

For polymers that demand maximum performance as well as film forming and adhesion, this versatile zinc borate is available in fine and extra-fine grades.

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Firebrake 500 logo

Stable up to 1112°F (600°C), this anhydrous zinc borate can be used in polymer systems that require very high processing temperatures.

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Ammonium pentaborate by U.S. Borax logo

Effective in intumescent coatings. It functions as both an inorganic blowing agent and a glass-forming compound.

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More about Borates in Polymers and coatings

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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 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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