ATH is a non-halogenated flame retardant filler produced from the same Bayer process used to refine bauxite into alumina, and research directly measuring its effect in a polymer composite shows a clear trade-off: it meaningfully cuts peak heat release, but only at a loading level that also cuts mechanical strength substantially. This page covers that trade-off and where ATH’s flame-retardant mechanism comes from.
What is it?
ATH (aluminum trihydrate, Al(OH)3) is a filler used mainly as a non-halogenated flame retardant in polymer compounds. Per the U.S. Geological Survey’s Mineral Commodity Summaries 2025, roughly 76% of bauxite consumed is refined via the Bayer process into alumina or aluminum hydroxide, with U.S. alumina production estimated at 810,000 tons in 2024; about 69% of that alumina went to primary aluminum smelters, with the remainder going to nonmetallurgical products such as abrasives, ceramics, chemicals, and refractories.
Why should I use it?
- ATH measurably reduces peak heat release in a tested polymer composite, backed by direct thermal and fire-testing data — see “How it’s used” and Limitations.
- Its flame-retardant action comes from a genuine chemical mechanism (endothermic decomposition releasing water vapor), not just inert bulk filling — see “How it’s used.”
How it’s used
In plastics and polymer compounds — including cable and wire insulation and sheathing made from polymers like EVA — ATH works by decomposing endothermically at high temperature into aluminum oxide and water vapor. A 2025 peer-reviewed thermogravimetric study found raw ATH begins decomposing around 243°C, with significant mass loss continuing to about 359°C; the released water vapor dilutes the flame and lowers combustion temperature, while the resulting aluminum oxide forms a protective layer on the material’s surface that limits further heat and oxygen transfer.
Limitations — when it isn’t the right choice
- ATH needs a high loading level to work well, and that same loading level can substantially weaken the material’s mechanical properties. The same 2025 study tested raw ATH at a 50 wt% loading in an EVA composite: peak heat release rate in cone calorimeter testing dropped 62.2% compared to unfilled EVA (from 1027 to 388 kW/m²), but tensile strength dropped 74.4% in the same formulation (from 12.5 to 3.1 MPa). The study describes ATH’s flame-retardant efficiency as generally inferior to organic flame retardants, “necessitating a high loading exceeding 50 wt% to achieve the desired flame retardant performance.” This means ATH’s fire-performance benefit and its mechanical-strength cost are directly linked at the loading levels needed for real effectiveness; these figures are specific to this EVA formulation and should be checked against the actual polymer system and loading level being used, not assumed to transfer directly to other resins like PP or PVC.
