Polyester is a category of polymers, or, more specifically condensation polymers, which contain the ester functional group in their main chain. Usually, polyester refers to cloth woven from polyester fiber. Polyester clothing is generally considered to have a "less natural" feeling to it compared to natural fibers. Polyester fibers are often spun together with fibers of cotton, producing a cloth with some of the better properties of each.

Although polyesters do exist in nature (e.g., in the cutin of the plant cuticle), polyester generally refers to the large family of synthetic polyesters (plastics) which includes polycarbonate and  above all polyethylene terephthalate (PET). PET is one of the most important thermoplastic polyesters.

Polyester is combustible but due to its thermoplastic nature, it tends to shrink away from the flame source and often self-extinguishes.

Polyester is also widely used as a finish on high-quality wooden products like guitars, pianos and vehicle/yacht interiors (Burns Guitars, Rolls Royce and Sunseeker are examples of companies that use polyester on their products). The thixotropic properties of the sprayable form of polyester make it ideal for use on open grain timbers as it can quickly fill the grain and has a high build film thickness per coat. The cured polyester can then be sanded and polished to a high-gloss, durable finish.