A review of technological developments in the polyester fiber sector discusses polybutylene terephthalate(PBT) fibers, polytrimethylene terephthalate(PTT) fibers, polyethylene naphthalate(PEN) fibers, biopolyester fibers, and other biodegradable polyester fibers. Important properties include tenacity, elongation, modulus, melting point, glass transition temperature, and density. Although patents for PBT date back to 1941, new interest in this fiber exists due to its excellent elasticity, which has advantages in stretch and comfort apparel. PTT combines the advantages of nylon and polyester and is superior to polypropylene in a range of applications. PEN can be used in diverse industrial fabrics, including sails, filters, and containers, but the high costs of raw polymaterials has impeded market growth. The most important biopolyester is poly(L-lactic acid), which is derived from agricultural byproducts and is biodegradable. It has the greatest potential of all biodegradable polymers because of its superior properties. 60 refs.