Late last year, several high-profile structural fires grabbed news headlines, renewing the focus on fire safety.
These unfortunate events reinforce why wood must be treated with proven flame-retardant additives, including boron, to save lives and construct safer buildings.
How borates protect wood from fire
For decades, manufacturers have applied borates to cellulosic materials to combat their natural propensity for combustion.
In wood and engineered wood products, borate flame retardants work by interfering with the chemical and physical processes that drive combustion.
Wood combusts in two modes:
- Primary: Visible flames are present
- Secondary: Flames are absent (glowing or smoldering)
Primary
As wood is exposed to heat, it thermally degrades and releases combustible gases that feed flame growth.
Borates disrupt this process by promoting char formation on the surface, creating a protective barrier that limits oxygen access and slows the release of flammable gases. This reduces flame spread and slows the fire’s growth, providing additional time for safe evacuation from buildings.
Secondary
Characterized by glowing or smoldering, secondary combustion can persist long after flames have subsided, increasing risk of re-ignition.
Borates are particularly effective in this scenario. By altering the thermal decomposition pathway of wood, borates suppress smoldering reactions and reduce the ability of heat to propagate through the material, which helps limit prolonged burning.
Learn more about boron in fire retardancy
Wood and composites that benefit from borate fire retardants
Borate-based flame retardants are used across a range of modern wood materials, including:
- Lumber
- Medium density fiberboard (MDF)
- Cross-laminated timber (CLT)
- Oriented strand board (OSB)
- Plywood
- Wood-fiber plastic composites (WPCs)
- Other engineered wood products
Each behaves differently under fire conditions due to variations in structure, resin systems, and manufacturing processes.
As a result, flame retardant additives must perform reliably across wood materials while still supporting compliance with performance standards such as a class A ASTM E84, EN 13501, and other regional requirements.
Material-specific considerations for fire retardancy
Different materials and manufacturing processes require different flame retardant formulations.
Solid wood lumber and plywood: Pressure treatment with borate-based solution provides high retention and core penetration. A soluble borate needs to be used. The high solubility of U.S. Borax’s Polybor®, provides a high boron concentration and retention in the wood.
Engineered wood products (particleboard, MDF, OSB): Borates can be mixed with the woodchips or incorporated in the resin as well as applied with a liquid solution. Our Firebrake® ZB product is a fine powder that can disperse effectively to provide good fire performance.
Wood plastic composites: These materials combine wood and polymers, making Firebrake ZB a well-suited choice for fire performance in both without disrupting processing.
Right product, right concentration
Achieving fire safety compliance involves both selecting an effective product and integrating it deep into the wood. U.S. Borax products are fully refined to deliver a consistent boron concentration to ensure formulation success.
Polybor is a proven borate flame retardant with versatile application. It can be added as a dry powder or pressure treated as an aqueous solution to ensure uniform distribution.
Explore more products for fire retardancy
Need fire retardant formulation help?
Our technical experts work closely with manufacturers to meet fire safety needs. We provide guidance on:
- Selecting the right product
- Developing fire retardant formulations
- Supporting product quality and performance
For more than 50 years, U.S. Borax has been a global leader in boron flame retardants for wood, and we have extensive knowledge of fire retardancy standards.
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