What is antimony trioxide and why is it in polyester?

Antimony trioxide is a chemical compound used as a catalyst in the production of polyester (PET) fiber. Virtually all polyester fabric contains residual antimony from the manufacturing process. Antimony is a heavy metal classified as a possible carcinogen by the International Agency for Research on Cancer, and it can leach from polyester fabric under conditions of heat and moisture.

Studies have shown that antimony leaches from polyester at measurable rates, with release increasing when the fabric is exposed to sweat, body heat, and UV light. This means that wearing polyester activewear during exercise or sleeping on polyester sheets creates conditions that maximize antimony transfer to the skin. Drinking water stored in PET bottles also contributes to antimony exposure through the same leaching mechanism.

Natural fibers do not contain antimony because it is not used in their production. Choosing Tencel, organic cotton, merino wool, or linen for garments and bedding eliminates antimony exposure from textiles entirely. ONDU curates brands using these natural alternatives so your clothing works for your health rather than introducing heavy metal exposure.