Polyester is a synthetic, man-made fabric derived from petroleum-based plastics (specifically, polyethylene terephthalate or PET). It is one of the most widely used fibers in the world today..Polyester 65% cotton 35% : 150 gsm / 190 gsm / 210 gsm / 245 gsm / 270 gsm Cotton 60% polyester 40%: 150 gsm / 190 gsm / 210 gsm / 245 gsm / 270 gsm Cotton 100% : 150 gsm / 190 gsm / 210 gsm / 245 gsm / 270 gsm / 300 gsm Cotton 50% polyester 50%: 180gsm