Magnesium hydroxide is a new type of filling flame retardant that releases bound water through thermal decomposition, absorbs a large amount of latent heat, and lowers the surface temperature of the composite material it fills in the flame. It has the function of inhibiting polymer decomposition and cooling the produced combustible gas. The decomposed magnesium oxide is also a good refractory material and can help improve the fire resistance of synthetic materials. At the same time, the water vapor it releases can also be used as a smoke suppressant, which is recognized as an excellent flame retardant in the rubber and plastic industry with three functions of flame retardancy, smoke suppression, and filling.