For years, I resisted identifying yarns by whether they were S or Z twist. “How could you possibly know whether you’re holding the yarn right-or-wrong-side up, I said to myself. (And I’ve heard others say it, too.) Often, I learn things when I have to teach something and this time it was for collapse weaving with overtwisted yarns. My toilet paper demo was a big help. I can’t remember how I thought it up.
What is S & Z?
Yarns have two directions of twist: S and Z. To see the direction of twist of a yarn, look for diagonal lines.
How to tell the direction.
Hold a length of the yarn taut. Look at it closely. You’ll see that the surface of the yarn spirals (note the diagonal lines). If the diagonal slants the same way as the line forming the middle of the letter S, then we say it has S twist. If it slants the same way as the line forming the middle of the letter Z, then we say it has Z twist. That is why the twists are named as they are. The seine twine in the photo shows S twist.
You can see how the diagonal lines are formed when you look at the toilet paper demonstration again. Which one shows S twist? Which one is the Z? Read on.
What to look for.
Look for the bars in the two letters: S & Z. See that the bar in the S goes on a diagonal like the back slash on the computer keyboard: \. Also see that the bar in the letter Z goes in the same direction as the forward slash: /.
Does it matter if the yarn is upside down?
Here is a gorgeous black cord I brought back from Bhutan (I think). Note where the tassel is in the photo. I see that the diagonal lines are going in the Z direction here. What will happen when I turn it upside down? See the next photo.
Now the tassel shows that I’ve turned the cord upside down, so-to-speak. It’s still Z twist! No change in direction! No matter which way you turn a yarn or look at it, the twist will always look the same!!
Here’s a quick way to check S & Z that always works. (The way I do it.)
Knowing that most yarns are twisted in the S direction, and that the right hand is the dominant hand for most people, swing your right hand across your body. Start the swing with your hand at your side and swing it towards your left shoulder. That is the same diagonal of S twisted yarn! So, if the yarn in question has the same diagonal as you do when you swing your right hand, it’s an S-twist yarn. Swinging your left hand across your body gives you the diagonal for Z twisted yarns. When I’m in a yarn shop, I don’t actually swing my arm—I just swing my hand across my chest—right for S direction and left hand for the Z direction.