Flax tow has had many purposes over the years. Comprised of the shorter fibers left after hackling the flax, tow like this can be spun into twine, used for starting fires, or most commonly among the historical community, for cleaning guns.
I added this to my fire-starting kit and the cleaning supplies for my musket. I used it for the latter purpose recently. At the range, I treated it with Ballistol and water. It did a good job of removing fouling between shots.