Yes, FLANNELS is a Scrabble word!

Letter values in Scrabble US: F 4, L 1, A 1, N 1, N 1, E 1, L 1, S 1.

Is it a valid word?

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

a soft light woolen fabric; used for clothing
bath linen consisting of a piece of cloth used to wash the face and body
(usually in the plural) trousers made of flannel or gabardine or tweed or white cloth

Also: face cloth.