The origin of mystic fibres, thread and cloth are wreathed in mystery. There's little to no mention in any written histories, which - on its own - seems unlikely. It is not a subtle material. There should be log after log of merchants trading it, or actively avoiding trading it.
It leads me to believe that the mystic material is an elaborate troll. It's a plant - and I don't mean that in the floral definition. I think someone has introduced it as a joke, and I have a list of potential culprits. Brassica Prime: you are number one on that list.