Flame Retardants: Types, Selection & Bulk Supply

A cable jacket that has to pass a vertical burn test. A flexible foam that a furniture flammability standard will not let through. An engineering plastic that needs a fire rating without the chlorine its OEM customer has banned. Every one of these is a flame-retardant problem, and solving it comes down to matching the right additive chemistry to the polymer, the process temperature, and the fire test you have to pass.

The short version: A flame retardant is an additive (or, less commonly, a reactive co-monomer) that interrupts combustion, either in the gas phase (scavenging the radicals that feed the flame) or in the condensed phase (forming a protective char or releasing water to cool and dilute). The major families are phosphate esters (versatile, many double as plasticizers), metal hydroxides such as alumina trihydrate and magnesium hydroxide (cheap, endothermic, used at high loadings), intumescent systems (an acid source, a carbon source and a blowing agent that build an expanding char), nitrogen synergists (melamine and its salts), boron compounds, and antimony trioxide (a synergist that boosts halogenated systems, not a standalone). Selection is driven by the polymer, the process temperature, the loading you can tolerate, the fire test, and increasingly by whether the application requires a halogen-free solution.

What is a flame retardant?

Combustion needs three things in a self-sustaining loop: heat, fuel (the volatile fragments a polymer gives off as it decomposes) and the chain-carrying free radicals in the flame. A flame retardant breaks that loop by acting on one or more of them. Some work in the gas phase, releasing species that quench the flame’s radicals so less heat returns to the polymer. Others work in the condensed phase, promoting a carbonized char layer that shields the polymer underneath and starves the flame of fuel, or decomposing endothermically to absorb heat and release water vapor that dilutes the combustible gases. Most are additive (blended into the polymer during compounding); a smaller set are reactive (built into the polymer backbone, so they cannot migrate out). Identity and property data for individual compounds are published at primary sources such as PubChem.

Additive vs reactive, and the halogen-free shift

Two distinctions frame almost every selection. The first is additive vs reactive: additive flame retardants are simpler and lower cost but can migrate, bloom or be extracted over time; reactive types are bound into the polymer and are permanent but require a compatible chemistry. The second is halogenated vs halogen-free. Halogenated (brominated and chlorinated) flame retardants are highly effective gas-phase agents, but many markets and OEMs have moved toward halogen-free systems for end-of-life, smoke and regulatory reasons. Phosphate esters, metal hydroxides, intumescent and nitrogen systems and boron are all halogen-free routes. Regulatory status varies by region, substance and end use, so confirm the status of any specific product for your market and application.

The flame-retardant families

Phosphate esters — versatile, often dual-function plasticizers

Phosphorus-based liquids and solids that act mainly in the condensed phase (char promotion) with some gas-phase activity, and many of which also plasticize the polymer, doing two jobs at once. They are the core of the RawSource line card. The workhorses are triethyl phosphate (TEP) and trimethyl phosphate (TMP) (low-viscosity, also used as solvents and intermediates), the triaryl phosphates triphenyl phosphate (TPP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP) and isopropylated triphenyl phosphate (IPPP), and the alkyl-aryl plasticizer-FRs cresyl diphenyl phosphate (CDP), isodecyl diphenyl phosphate (IDDP) and 2-ethylhexyl diphenyl phosphate (DPO). Trialkyl grades tris(2-ethylhexyl) phosphate (TOF), tris(2-butoxyethyl) phosphate (TBEP) and triisobutyl phosphate (TIBP) serve plasticizer, anti-foam and low-temperature roles, tributyl phosphate (TBP) is a solvent/anti-foam phosphate, and tris(1-chloro-2-propyl) phosphate (TCPP) is the chlorinated phosphate widely used in polyurethane foam. For high-char engineering-plastic use there is the caged bicyclic phosphate (PEPA).

Metal hydroxides — cheap, endothermic, high loading

Mineral fillers that decompose endothermically, absorbing heat and releasing water that cools the polymer and dilutes the fuel gases, while the residual oxide forms a protective layer. They are inexpensive and halogen-free but are used at high loadings (often 40–60%), which affects mechanical properties. Aluminum hydroxide (ATH) is the most-used flame retardant by volume worldwide; magnesium hydroxide (MDH) decomposes at a higher temperature, so it suits polymers processed above ATH’s decomposition point. Magnesium oxide and the smoke-suppressing hydrotalcite round out the mineral set.

Intumescent systems — an expanding char barrier

Intumescent flame retardants are a three-part package: an acid source, a carbon source and a blowing agent that together swell into a thick, insulating char when heated. Ammonium polyphosphate (APP) is the acid source and backbone of most halogen-free intumescent coatings and compounds; pentaerythritol is the classic carbon/char former; and a nitrogen source such as melamine provides the blowing gas. This trio is the heart of intumescent fire-protective paints and many halogen-free polyolefin compounds.

Nitrogen synergists — melamine and its salts

Nitrogen-based additives release inert gases that dilute the flame and promote char, and they work especially well in nitrogen-containing polymers. Melamine, melamine cyanurate (the standard flame retardant for unfilled nylons) and melamine-formaldehyde resin cover this space, often paired with phosphorus for a phosphorus-nitrogen synergy.

Boron compounds — char, glass layer and afterglow control

Boron additives promote char, form a protective glassy layer and suppress afterglow and smoke. Zinc borate is widely used as a synergist and partial replacement for antimony trioxide; boric acid and borax (sodium tetraborate decahydrate) are standard for cellulosic and wood treatments.

Antimony trioxide — a synergist, not a standalone

Antimony trioxide (ATO) has little flame-retardant effect on its own; it is a gas-phase synergist that sharply boosts the efficiency of halogenated flame retardants, letting formulators use less of them. It is therefore specified together with a halogen source, and is not part of a halogen-free system. Confirm regulatory status for your market and application.

Phosphinates and other engineering-plastic options

For glass-filled engineering plastics (PA, PBT) processed at high temperature, aluminum diethylphosphinate is a leading halogen-free, condensed-phase option, usually combined with a nitrogen synergist. Phosphate salts such as diammonium phosphate (DAP), monoammonium phosphate (MAP) and urea phosphate serve cellulosic, textile and wood fire-treatment roles.

How flame retardants work

How to select a flame retardant

Work through five questions. Polymer and process temperature: the additive must survive compounding and end-use temperatures, which is why MDH replaces ATH above its decomposition point and phosphinates suit high-temperature engineering plastics. Loading you can tolerate: mineral hydroxides need high loadings that change mechanics, while phosphorus and intumescent systems work at lower addition. The fire test: the standard you must pass (vertical burn, glow-wire, cone calorimeter, a furniture or cable standard) sets the target and often the family. Halogen-free or not: many OEMs and markets now require halogen-free, which points to phosphorus, mineral, intumescent, nitrogen and boron routes. Secondary function: a phosphate ester that also plasticizes, or a borate that also suppresses smoke, can do two jobs and simplify the formulation. Validate the final package with the actual fire test on your part, not on theory.

Where flame retardants are used

Buying flame retardants in bulk

RawSource sources the flame-retardant range direct from producers: the full phosphate-ester group (TEP, TMP, TPP, TCP, TXP, IPPP, CDP, IDDP, DPO, TBEP, TIBP, TBP, TCPP), the mineral hydroxides (ATH, MDH), intumescent components (APP, pentaerythritol, melamine and salts), boron compounds (zinc borate, boric acid, borax), aluminum diethylphosphinate and antimony trioxide synergist. Tell us the polymer, the process temperature, the fire test you must pass, your maximum loading, and whether the application must be halogen-free, and we will quote the right product or system with CoA, TDS and SDS per lot. Many of these products double as plasticizers or solvents, which is mapped alongside the building blocks in the amines guide for nitrogen synergists. Regulatory status, suitability and safe handling are the buyer’s responsibility; confirm them for your jurisdiction.

Frequently asked questions

What is a flame retardant and how does it work?

A flame retardant is an additive or reactive co-monomer that interrupts combustion. It acts in the gas phase by scavenging the radicals that sustain the flame, or in the condensed phase by forming a protective char or by decomposing endothermically to cool the polymer and release water that dilutes the combustible gases.

What are the main types of flame retardants?

The main families are phosphate esters, metal hydroxides (alumina trihydrate and magnesium hydroxide), intumescent systems (an acid source, a carbon source and a blowing agent), nitrogen synergists (melamine and its salts), boron compounds, phosphinates for engineering plastics, and antimony trioxide as a synergist for halogenated systems.

What is a halogen-free flame retardant?

A halogen-free flame retardant contains no bromine or chlorine. Phosphate esters (non-chlorinated grades), metal hydroxides, intumescent and nitrogen systems, boron compounds and phosphinates are all halogen-free routes that many OEMs and markets now require. Confirm regulatory status for your specific product and market.

What flame retardant is used in polyurethane foam?

Polyurethane foam typically uses liquid phosphate esters, with tris(1-chloro-2-propyl) phosphate (TCPP) common in rigid and flexible foam and triethyl phosphate (TEP) used where a low-viscosity, halogen-free phosphate is wanted. The right grade depends on the foam system and the fire test.

Why is antimony trioxide used with flame retardants?

Antimony trioxide has little effect alone; it is a gas-phase synergist that greatly increases the efficiency of halogenated flame retardants, so formulators can reach a fire rating with less total additive. It is always used together with a halogen source, never as a halogen-free solution.

What is an intumescent flame retardant?

An intumescent system is a three-part package — an acid source such as ammonium polyphosphate, a carbon source such as pentaerythritol, and a nitrogen blowing agent such as melamine — that swells into a thick insulating char when heated, shielding the substrate. It is the basis of most halogen-free fire-protective coatings.

How do I choose a flame retardant for plastics?

Start from the polymer and its process temperature, the fire test you must pass, the loading you can tolerate without losing mechanical properties, and whether the application must be halogen-free. Mineral hydroxides suit polyolefins at high loading, phosphinates and melamine cyanurate suit engineering plastics, and phosphate esters suit PVC and foams. Confirm by running the actual fire test on your part.

Editorial note. This article is general technical guidance for industrial and professional buyers and formulators. Mechanisms, family characteristics and selection guidance are typical, generalized references to validate on your own line and against the relevant fire test; the Certificate of Analysis and Technical Data Sheet govern the grade you buy. Nothing here is a safety, health or efficacy claim. Flame retardants have specific handling and hazard requirements and several are subject to evolving regulation — always consult the current Safety Data Sheet (SDS) before handling, and confirm regulatory status, restrictions and suitability for your application and jurisdiction. RawSource makes no warranty, express or implied, and assumes no liability for use of this information.

RawSource Editorial

Commercial & Sourcing Desk