Throughout the years of using the aluminum silicate fiber material, it is often found that the actual temperature does not exceed the material's temperature range, yet the fiber material experiences severe shrinkage and powdering. Chemical analysis shows that Al2O3 meets product specifications, but SiO2 is below par, and the contents of Fe2O3, CaO, MgO, Na2O, K2O, and other impurities are severely excessive. These impurities are low-melting-point oxides, and an excess of low-melting-point oxides will lower the eutectic point of the aluminum silicate fiber material. If the content of impurities other than Al2O3 and SiO2 reaches above 3.5%, it will lower the actual service temperature of the aluminum silicate fiber material by nearly 100°C compared to being controlled within 1%. Therefore, when selecting aluminum silicate fiber materials, we must not only check the Al2O3 composition but also strictly control the content of other impurities.