Antimony trioxide is an industrial chemical and also occurs naturally in the environment. Antimony trioxide is primarily used in combination with other compounds to provide flame retardant properties. Flame retardants used in household items such as mattress covers, furniture and carpets may contain antimony trioxide. Antimony trioxide is also used in the manufacturing of a plastic material known as polyethylene terephthalate (PET). In addition, Antimony Trioxide can be used as an opacifying agent for glasses, ceramics and enamels and in it can be found in specialty pigments.