Polyester is a natural chemical (found in plants) and now synthesized for fabrics used in everyday life. Polyester is used in apparel, furnishings and industrial goods like robes and tough fabrics.
Polyester is used for insulation in pillows also its ability to feel soft and comforting. It is also used in clothes. Its usage has dwindled recently. In the 80s the fabric was very popular and still has strong associations to that era. These days it is used in retro style clothing, hunting jackets, and even in the labs using synthetic materials. Its usage is more functional than for fashion in most cases.