The main use of antimony is that its oxide antimony trioxide is used to make refractories. Except for halogen containing polymer flame retardants, it is almost always used with halide flame retardants. The formation of antimony halide from antimony trioxide can slow down combustion, which is the reason why it has flame retardant effect. These compounds react with hydrogen atoms, oxygen atoms and hydroxyl radicals, and finally extinguish the fire. These flame retardants are commercially used in children's clothing, toys, aircraft and car seat covers. It is also used as an additive for polyester resin in the glass fiber composite (commonly known as fiberglass) industry, such as the engine cover of light aircraft. The resin burns in case of fire, but its combustion will stop automatically after the fire is extinguished.