Yes, FIBRES is a Scrabble word!

Letter values in Scrabble US: F 4, I 1, B 3, R 1, E 1, S 1.

Is it a valid word?

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

a slender and greatly elongated substance capable of being spun into yarn
any of several elongated, threadlike cells (especially a muscle fiber or a nerve fiber)
the inherent complex of attributes that determines a persons moral and ethical actions and reactions
a leatherlike material made by compressing layers of paper or cloth

Also: vulcanized fiber.