The Federal Trade Commission (FTC) defines polyester as “a manufactured fiber in which the fiber-forming substance is any long chain synthetic polymer composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephthalate units, and para substituted hydroxy-benzoate units.” 
Most polyesters are derived from polyethylene terephthalate (PET), which is ethylene glycol combined with either terephthalic acid or its methyl ester under high temperature and pressure.
A Simple Look at Polyester
Simply speaking, polyester is a manufactured fiber, which means that it is derived from substances that do not begin as fibers but are manufactured to become fibers. These fibers are then woven into a variety of products such as clothing, bedding, and furniture.
Polyesters can be natural such as those derived from plant cuticles but most are synthetic thermoplastics.
Benefits of Polyester
Because polyester fabric is derived primarily from synthetic fibers, it can have many beneficial properties such a natural resistance to wrinkles, shrinking, mildew, and chemicals. These properties make any garment an easy care, no hassle wardrobe choice.
“Rules and Regulations Under the Textile Fiber Products Identification Act.” Federal Trade Commission. N.p., n.d. Web. 5 Oct. 2011. <http://www.ftc.gov/os/statutes/textile/rr-textl.htm#303.6>.
“Polyester Fiber – Polyethyleneterephthalate – Polyethylene Naphthalate – Polyester Tow Fiber, Polyester Staple Fiber, Polyester Fiberfill, Polyester Textile Filament Fiber, Polyester Industrial Filament Fiber.” FiberSource: The Manufactured Fiber Industry. N.p., n.d. Web. 5 Oct. 2011. <http://www.afma.org/f-tutor/polyester.htm>.