Yes, POLYESTERS is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, L 1, Y 4, E 1, S 1, T 1, E 1, R 1, S 1.

Is it a valid word?

POLYESTERS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any of numerous synthetic resins; they are light and strong and weather resistant
a complex ester used for making fibers or resins or plastics or as a plasticizer
any of a large class of synthetic fabrics