What is Polyester?

Polyester is only one compound in a class of petroleum-derived substances known as polymers. Thus, polyester (in common with most polymers) begins its life in our time as crude oil. Crude oil is a cocktail of components that can be separated by industrial distillation.
Polymers are made by chemically reacting a lot of little molecules together to make one long molecule. The little molecules are called monomers and the long molecules are called polymers.
Like this:
O + O + O + . . . makes OOOOOOOOOOOOOOOO
Depending on which polymer is required, different monomers are chosen. Ethylene, the monomer for polyethylene, is obtained directly from the distillation of crude oil; other monomers have to be synthesized from more complex petroleum derivatives, and the path to these monomers can be several steps long. The process for polyester is made by reacting ethylene glycol and terephthalic acid.
The polymers themselves are theoretically quite unreactive and therefore not particularly harmful, but this is most certainly not true of the monomers. Chemical companies usually make a big deal of how stable and nonreactive the polymers are, but that’s not what we should be interested in. We need to ask, what about the monomers? How unreactive are they?
We need to ask these questions because a small proportion of the monomer will never be converted into polymer. It just gets trapped in between the polymer chains. Over time this unreacted monomer can escape, either into the atmosphere if the initial monomers were volatile, or by dissolving into water if the monomers were soluble. Because these monomers are so toxic, it takes very small quantities to be harmful to humans, so it is important to know about the monomers before you put the polymers next to your skin. Since your skin is usually moist, any water-borne monomers will find an easy route into your body.
Polyester is the terminal product in a chain of very reactive and toxic precursors. Most are carcinogens; all are poisonous. And even if none of these chemicals remain entrapped in the final polyester structure (which they most likely do), the manufacturing process requires workers and our environment to be exposed to some or all of the chemicals. There is no doubt that the manufacture of polyester is an environmental and public health burden that we would be better off without.
Polyester fabric is soft, smooth, supple – yet still a plastic.  It contributes to our body burden in ways that we are just beginning to understand.  And because polyester is highly flammable, it is often treated with a flame retardant, increasing the toxic load.  So if you think that you've lived this long being exposed to these chemicals and haven’t had a problem, remember that the human body can only withstand so much toxic load – and that the endocrine disrupting chemicals which don’t seem to bother you may be affecting generations to come. Source material - OEcotextiles
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