Singles need to be spun to the necessary diameter to achieve a final cord of desired diameter with the desired number of plies. For optimum results and ease, spin as fine and tight of singles as possible and ply them in combinations of threes to achieve bulkier cords that are round. I recommend Navajo plying. Core spinning offers the advantage of having the solid core of an inexpensive fiber and outer surface of an expensive fiber. Core spinning also provides a denser core that may be easier to spin and a lighter outer surface.
Most knots look best in a dense cord.
But knotting is not limited to dense cord and when combining knotting with garments not entirely desirable. The linen belt illustrates the denser cords. Re-spinning commercial yarns to make them suitable for knotting. Each of the following will be studied and discussed relative to the intended finished product. First add twist in the direction of the warps yarn's final ply.