Firebrake Flame Retardant Products

Unique zinc borates that combine the optimum effects of zinc and boron oxides

Firebrake ZB

Protection for polymers

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.

Firebrake 500

Polymer protection for high processing temperatures

Anhydrous zinc borate that has numerous applications as a fire retardant and is stable up to 600°C.
Both Firebrake® products can be fed to extruders, calenders, or injection molding equipment, much like other solid polymer additives.

Help Prevent Fire in Plastic and Rubber Compounds

Firebrake ZB has multi-functional fire-retardant applications in plastic and rubber compounds. Because Firebrake ZB releases its water of hydration at temperatures exceeding 554°F (290°C), it can be used in systems that require high processing temperatures. Firebrake ZB has a refractive index similar to that of most polymer systems, so it retains considerable translucency and enables the use of low pigment loading.

Video: Borates in fire retardancy


Firebrake in fire retardancy

Firebrake products are used in a variety of fire retardant applications. Watch the video >

Borate flame retardant additives are perfect for high process temperatures.

Stable Up to 600°C

Firebrake 500 is an anhydrous zinc borate for multi-functional fire retardant applications in a variety of polymers. Because it contains no water of hydration, it is stable up to 1112°F (600°C) and can be used in polymer systems that require very high processing temperatures.


​Firebrake ZB

Firebrake ZB is used as a flame retardant, char promoter, afterglow and smoke suppressant, and anti-arc agent in polymer systems, including:

  • Polyvinyl chloride
  • Nylon
  • Epoxy
  • Polyethylene
  • Polypropylene
  • Polyesters
  • Elastomers

Depending on the base polymer that you use and the fire protection standards that need to be met, you can use Firebrake ZB to partially or completely replace other fire-retardant additives such as antimony oxide. (In some systems, Firebrake ZB displays synergism with antimony oxide.) In halogen-containing systems, use three to 25 parts of Firebrake ZB per 100 parts of resin (phr). In halogen-free systems, the recommended level is in the range of 10 to 25 phr, normally used in conjunction with alumina trihydrate, magnesium hydroxide, or a silicone polymer. (In some cases, our technical team may be able to give recommendations for starting point formulations.)

For situations that demand maximum fire-test performance as well as film forming and adhesion, Firebrake ZB is available in fine and extra-fine formulations. The extra-fine grade has no particles greater than 12 microns (as determined by laser diffraction) and is suitable for more critical flame retardant applications.

Firebrake 500

Firebrake 500 is an anhydrous form of Firebrake ZB that is specially designed for applications in which no water evolution is permitted. You can use Firebrake 500 as a flame retardant, char promoter, and smoke suppressant in a variety of polymers, including:

  • High temperature polyamides (PPA) and polyamide 6.6
  • Polyetherketones
  • Polysulfones
  • Fluoropolymers
  • Polyesters

Firebrake 500 has a significant beneficial effect on the rate of heat release, a quality that is of special interest in aircraft applications. It can also function as a corrosion inhibitor in polymer processing.

Chemical and Physical Properties
  • Refractive Index: 1.58
  • Median particle size (laser diffraction):
    • Firebrake ZB Fine: ≤ 2.5 microns
    • Firebrake ZB-XF: ≤ 2.2 microns
  • Molecular weight: 434.67
  • Specific gravity: 2.77
  • Appearance: White, crystal like powder
  • Solubility: Less than 0.28% in water at room temperature
  • Stability: Thermally stable up to 554°F (290°C); can be hydrolyzed by strong acids and bases
Chemical Composition (Theoretical)
  • Boric oxide, B2O3: 48.05%
  • Zinc oxide, ZnO: 37.44%
  • Water of crystallization, H2O: 14.51%
  • Anhydrous equivalent: 85.49%
  • Containers: Products may be available in bulk, IBCs, or small bags


Available Grade
  • Granular
Store Firebrake 500 in a sealed container because of its tendency to gradually pick up surface moisture in high-humidity environments. This surface moisture is easily removed by heating at about 200°C. Additional Assistance
Have questions about how Firebrake 500 is working in your formulations? Contact our fire retardancy and polymer technical expert for help.
Chemical and Physical Properties

Refractive Index: 1.58

Median Particle Size: ≤12 microns (laser diffraction)

Weight Loss (TGA): 1.5% maximum to 400°C

Stability:  Thermally stable to >600°C; can gradually absorb surface moisture

Molecular weight: 371.62

Specific gravity: 2.6

Appearance: White, crystal like powder

Stability: The product is chemically stable and shows little tendency to cake.

Chemical Composition (Theoretical)

Boric oxide, B2O3: 56.20%

Zinc oxide, ZnO: 43.80%

Containers: Products may be available in bulk, IBCs, or small bags

Firebrake in Action

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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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