What is meant by 4 ply yarn? June 03 2019, 3 Comments

I see variations on this question asked frequently, so I thought I'd try and share my thoughts on it. The term 4 ply can be confusing to a lot of knitters and crocheters, whether you are new to yarn crafts or not. It can be used as a description of the yarn's thickness (weight), or its structure and is often combined with other, sometimes conflicting terms, when used to describe a particular yarn. So why is it so complicated?

Where does the term come from?

The dictionary definition of ply is

"a strand of yarn or rope"

When a yarn is spun, either by hand or by machine, the spinner has a choice of whether to create a single strand the thickness they need, or to create several thinner strands and combine them. This is done by twisting them in the opposite direction to the original spin and is called plying them. Plyed yarns are stronger than a single strand of the same thickness because of this structure. Its the same principle used for creating strong ropes for ships rigging or suspension bridges, just on a rather smaller scale.

A strand of 4 ply yarn with the plys separated
Structure of a 4 ply yarn

So, historically yarn was created out of standard thickness plys, or strands, and therefore describing a yarn by the number of these plys used gave a good indication of the thickness of the resulting yarn. The finest yarns were 1 or 2
ply (lace weight), DK was known as 10 ply and 4 ply lies somewhere in between. This was great and you could easily see that 2 strands of 4 ply are about the same thickness as DK, 2 strands of lace weight are about the same as 4 ply.

However, it is now more common to find yarn created from strands that aren't a standard thickness, from single strands of bulky weight yarn to very fine threads made up of many strands. This means a strand of yarn made up of 4 plys now
could vary between being a very fine cobweb weight to extra bulky. 4 Ply is now used as a description of the thickness of the yarn regardless of its structure.

Why does it matter?

Sometimes it is useful to know the structure of a yarn as well as its thickness. A plyed yarn has different properties to a single and the number of plys changes the shape of the yarn which can affect how it looks when knitted up, but the details are another whole blog post! It matters because its confusing not to know if a yarn described as 4 ply is made up of 4 plys, is fingering weight, or both!

We dye a couple of singles yarns, Selkino and Wriggle, which are both fingering weight, the rest are all plyed.

So, what is the best way to describe a yarn?

The most accurate way to describe a yarn's thickness is wraps per inch (WPI)
and this can easily be measured using a thick knitting needle (or similar) and a ruler or tape measure. Wrap the yarn snugly but not too tightly around your needle, making sure the strands lie next to each other but aren't too squashed. Measure 1" and count how many times the yarn is wrapped in that inch. This
is the WPI for that yarn. Different weights of yarn generally fall into the following ranges of WPI:

This gives a very accurate measure of yarn thickness for most yarns. The only difficulties are with fluffier yarns where it is difficult to wrap them closely enough to get an accurate WPI measurement.

I am going to try and update all the listing on the website to give the wpi of our yarns and their structure, although that will be ongoing as it takes time to go through all the existing products.