I have just ordered a huge amount of “2 ply” cones of wool and it brought up the question of what is ply? For the most part, it means the quantity of “strands” making up that piece of wool. When you have an 8ply yarn, you have a piece of wool that is made up of 8 strands twisted together. This in no way tells you how “thick” your yarn is though. A 2ply yarn might be thicker then an 8ply yarn, why? Because the 2ply has been spun to be bulkier then the 8ply.
In short, “ply” has nothing really to do with the thickness of your yarn, and with more and more yarns becoming available from outside Australia and New Zealand we can no longer rely on labels saying 8ply, 4ply, 10ply etc when selecting yarn. There is a little more discussion on Pearl Bee about this topic, with some very important clarification and information provided by the mystery “Pat”.
Pat commented that “there was a standard as to measurement of yarns. It was based on the number of skeins of yarn that can be spun from one pound of fibre. This is dependent on how fine the spinner can spin; a larger number means a finer yarn (of wool). This gets confusing. Wool had a different system than cotton which was different than linen, and acrylic wasn’t even considered then.
Today there are several different methods of measurement: tex in Europe, 1-8 by the Yarn Council of America, ply system in Australia. The best seems to be wraps per inch — how many threads laid side by side in one inch. Another standard is yards per pound (ypp), or metres per kilogram (mpk). Obviously, 1500 ypp would be finer yarn than 1200 ypp.
Cotton usually uses a numbering system: 2/8 means a yarn of 2 plys each being of size 8 (standard measurement in cotton). 2/16 would be a finer yarn, being 2 plys but of size 16. 4/8 is a thicker yarn: 4 plys of size 8. 8/2 is 8 plys of a size 2 yarn.
And then we get into compound and cabled yarns; these are all differences in construction– nothing to do with size.”