Polyester fiber, commonly known as "polyester". It is a kind of synthetic fiber, PET fiber for short, which is made of polyester by polycondensation of organic binary acid and binary alcohol. Invented in 1941, it is the largest variety of synthetic fiber at present. The biggest advantage of polyester fiber is good wrinkle resistance and shape retention, with high strength and elastic recovery ability. It is firm, durable, wrinkle resistant, and ironless. It's the material for making knitted sherpa fleece fabric.