Polyester is a plastic
Polyester is a synthetic (petroleum-based) aka. oil.
It can be difficult to remove stains from polyester and it does not breathe as well.
To make polyester, ethylene glycol and dimethyl terephthalate are mixed together. The chemical reaction results in bisterephthalate. This substance is heated to 270° Fahrenheit (132° Celsius), where it reacts again to form polyethylene terephthalate. Like many chemical reactions that result in polymers, the polyester making process results in unhealthy off gassing, and protection should be worn while making PET.
Polyester does contain the carcinogenic heavy metal antimony and also contains PBTs.
PBTs are chemicals that are Persistent (they do not biodegrade or photodegrade), Bioaccumulative (they accumulate in body tissue and fats), and Toxic.
The uses of antimony and PBTs in polyester clothing are some of the reasons that polyesters can be harmful and unhealthy to wear.
Polyesters, nylons and acrylics are synthetic fabrics made from petroleum, a gooey and non-renewable resource.
Acrylic is a suspected carcinogen.
Plastic soda bottles, which are produced from polyesters.