Aluminum hydroxide and magnesium hydroxide are two widely used inorganic flame retardants, especially in plastics, rubber, coatings, and cable materials. Both are valued for their low toxicity, low smoke generation, and environmental friendliness compared with many halogenated flame retardants. However, they differ in thermal behavior, processing requirements, and practical applications, which makes each suitable for different formulation needs.Aluminum hydroxide, also known as ATH, is one of the most common mineral flame retardants. Its flame-retardant effect comes from an endothermic decomposition reaction. When heated, ATH begins to decompose at around 180–200°C, releasing water vapor and absorbing heat. This process helps cool the material and dilute combustible gases in the flame zone. At the same time, the remaining aluminum oxide forms a protective layer that can slow further combustion. ATH is especially useful in materials processed at relatively low temperatures because of its lower decomposition temperature. It is often used in polyethylene, ethylene-vinyl acetate, unsaturated polyester, and cable compounds. Another advantage of ATH is its good whiteness and fine particle availability, which make it attractive for products requiring appearance quality.Magnesium hydroxide, or MDH, works in a similar way but has a higher decomposition temperature, usually around 330–350°C. This means it can tolerate higher processing temperatures than ATH, making it more suitable for engineering plastics and materials that require elevated compounding temperatures. Like ATH, MDH absorbs heat during decomposition and releases water vapor, which reduces the temperature of the burning material and suppresses flame spread. The magnesium oxide residue also contributes to a protective barrier. Because of its higher thermal stability, MDH is often preferred in applications such as polypropylene, polyamide, and high-temperature wire and cable systems.When comparing the two, the main difference is temperature resistance. ATH decomposes earlier, so it is better for low-heat processing systems. MDH decomposes later, so it is better for heat-resistant formulations. Another difference is loading level. Both minerals often need to be used in relatively high amounts to achieve effective flame retardancy, which can affect mechanical properties such as flexibility, tensile strength, and impact resistance. In some cases, surface treatment, particle-size control, and coupling agents are used to improve compatibility with polymers and reduce these negative effects.In terms of safety and environmental performance, both are considered excellent choices because they are non-halogenated and produce less toxic smoke and corrosive gases during combustion. This makes them suitable for applications where fire safety and environmental regulations are important.In summary, aluminum hydroxide and magnesium hydroxide are both effective, eco-friendly flame retardants, but their different decomposition temperatures determine their best uses. ATH is ideal for lower-temperature processing, while MDH is better for higher-temperature materials. Choosing between them depends on the polymer type, processing conditions, and required fire performance.