S vs. Z Twist

What is it thread twist and why does it matter? Our thread begins as roving. Roving is the cotton or linen fibers that has been prepared for spinning. It is not very strong in this state. So, the roving is spun into long pieces, called staples, which “tangles” all the roving together making it stronger. Then two or more of those staples are spun, or twisted, together to create a stronger thread, called a ply.

The direction of the twist is important. If you hold the roving at one end and you twist it to the left, you create an “S” twist. If you twist it to the right, you create a “Z” twist.

S vs. Z Twists S vs. Z Twist

It is a two-step process to create most embroidery thread. The staples are spun together with the primary twist first in a “Z” twist, then with an “S” twist. Most of the time, the twist is not mentioned in the product information. For example, Sullivans says their floss is “100% Egyptian cotton with reverse twist to provide virtually knot free and tangle free”.

For embroidery, it doesn’t really make a difference for some stitches such as satin and chain. But for stitches like stem stitch and bullion knots it can make a difference. Remember how you sometimes have to stop and let your needle and thread dangle to unwind? This twisting motion as you stitch can also untwist your thread. If you keep stitching, your thread will become a little fuzzy. Some thread companies will tell you which twist their thread is, but for others you may have to look at the thread to find out.

Here are four threads:

Thread Sample Thread Sample Comparison

DMC Floche #799, DMC Pearl Cotton Size 5 #931, DMC Floss #932, and EdMar Lola #112. The first three have an “S” Twist and the last one has a “Z” twist. Can you see the difference?

EdMar threads have a “Z” twist. This is very important to know especially when creating bullion knots. When making a bullion knot with a “Z” twist thread, you must wrap your thread around the needle in a clockwise direction. If you wrap in the other direction, the thread begins to unwind, especially for a long bullion. To make a bullion knot with an “S” twist thread, you need to wrap in a counterclockwise direction.

To understand what these mean, let’s look at those same four threads from earlier. First, each thread was used to stitch a satin block on 14-count Aida. Three strands of the floss were used. Do you think the twist in this instance makes much of a difference?

Satin Stitch Example Satin Stitch Example

What happens if we stitch a stem stitch and an outline stitch? When you do a stem stitch, your needle is always above the thread line. If your needle is below the thread line it becomes an outline stitch. For every thread, the stitch on the left is a stem stitch and the stitch on the right is an outline stitch. You can see where the twist does make a difference in how crisp the stitch appears.

Stem Stitch Example Stem and Outline Stitch Example

Lastly, let’s look at the bullion knot. For every thread, the bullion on the left is done with a clockwise wrap. The bullion on the right is done with a counterclockwise wrap. Which direction do you think looks best for each? Experiment yourself using threads from your stash and see what you think. If you do try your own tests, we’d love to see your findings and results!

Bullion Stitch Example Bullion Stitch Example

Egyptian vs. Pima Cotton

We’ve been talking mostly about cotton threads. Cotton is a natural fiber, related to the hibiscus plant. The seeds are planted in the spring and it grows into a bush about three feet tall. Flower buds are called “squares” and start as a cream color. Then the squares change to yellow, pink, and then dark red. About three days later the buds fall off to reveal a green pod called a cotton “boll”. The fibers inside continue to grow and expand until the boll splits open. The mature cotton is harvested by machine and starts its process to become cotton thread.

Cotton Boll Cotton Boll

Most of our cotton thread is either Egyptian or Pima cotton. Egyptian cotton is the finest, longest staple cotton, grown in the Nile River Valley. It is exceptionally soft. Pima cotton also is fine, long and staple cotton. It is named after the Pima Native American tribe who grew cotton in Arizona. Pima cotton is primarily grown in the United States. It is generally less expensive than Egyptian cotton.

Ply vs. Strand

This can be confusing! What is the difference? This information was previously provided by Marion Scoular:

Ply: “The finest component of a thread is called a staple. Staples are twisted into plies, two or more of which are then twisted into threads. “Ply” is a verb and “plies” is a noun. Plies are twisted together to create a strand, and a strand can be separated.”

Strand: “A strand is a single thread, regardless of how many plies it contains. Strands may be tightly twisted multiples, which can be separated (stripped) and used in the desired number, laying as you stitch. Plies are not meant to be separated.

Here is how some thread manufactures describe their threads:

  • DMC Floss: Comprised of 6 size 25 easily separated strands
  • Dinky-Dyes Silk floss: 6 stranded spun silk
  • Caron Collection Watercolours: A three-ply hand-dyed pima cotton
  • Rainbow Gallery Splendor: A 12-ply silk that is composed of three 4-ply bundles twisted together.
  • Weeks Dye Works Floss: hand over-dyed, 6-stranded Egyptian cotton fiber

Perle vs. Pearl

Which is correct? Either spelling is fine. “Perle” is French for “pearls”. DMC says the thread is called pearl cotton “because of the twist” perhaps because it creates a strand that looks like pearls. Another source says it is because the thread is mercerized to give it a pearlescent sheen.

What does mercerized mean?

This is a process applied to linen and cotton threads and fabrics. What does that do to our threads

First, it adds luster. This is the amount of light that reflects off the thread. The smoother the thread is, the better the luster. Mercerization makes the thread smoother and reduces the amount of lint.

Second, it makes the fibers more water soluble, which means it takes dyes better and the dyed color is darker. A side benefit is that the dye keeps its color longer when washed.

Third, it increases the strength of the fiber and gives the thread a resistance to mildew.

Mercerization is not a new process. John Mercer started working with various chemicals early in the 1800’s. In the 1880’s he applied for a British patent for the process. The spun threads were treated with various chemicals, including sodium hydroxide or sulfuric acid, but it didn’t add the luster we are used to.

Horace Lowe found that if you treated the threads while they are under tension, it changes their appearance, adding that luster. He filed his patent in the 1890’s.

We don’t usually feel the difference between mercerized and unmercerized thread, but if you compare a towel made from unmercerized thread to one that is mercerized, the unmercerized towel is much softer on our skin.

Where are our supplies made?

According to the US Federal Trade Commission, a product has to be “all or virtually all” made in the United States to have the “Made in America” designation. That is not the same in other countries. The European Customs Code says a product made in two or more countries is considered to originate in the country where the final transformation or substantial work took place. Some countries take that even further. For example, if a French company commissions the product and it is totally made in another country, it can claim to be made in France.

Hopefully this gives you a little insight into that most important piece of our stash: our threads!


We hope this guide makes your stitching easier and more enjoyable!

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