Fibre grows in soft, white buds on plants found close to water. Look around river banks and lakes in order to find it.
Fibre is collected with a Sickle. You can harvest normal quality Fibre by using a Sickle 1 tier below. To harvest higher rarity you need a Sickle on the same tier or one tier lower.
Fibre must to be refined into Cloth at a Weaver before you can use it to craft armor or accessories.