The theory is that when you throw the yarn in knitting you untwist a bit if it is plied in the wrong direction. then for weaving, the twist from unwinding off the shuttle will either twist more or less depending on which way it is plied. so the weaving yarn should be plied opposite from knitting. (S then Z, I guess)
I never found much difference, and use whatever I have anyway I want. We can get too worried about all this. I would not think the yarn was defective if it made a lovely garment. Nancy
