If the 2-ply and 3-ply are the most normal of yarns, 5-ply is one of the most unusual. I can honestly say I’ve never spun one before.
Now, if I had wanted to learn a little more about 5-ply, I would have spun much finer singles. These same singles which made a 14 WPI 2-ply made a 7-WPI 5-ply. While that isn’t super bulky, it is bulky.
The squoosh factor on this yarn is pretty great. It seems that the extra plies don’t just introduce more wool; they introduce more air. It would take some more advanced geometry than I am capable of to really measure this, but I am curious: are multi-plies always less dense (excluding other factors)?
This chapter is not about color, but I can’t help but notice that all five colors together look much softer. The 3-ply had the brightest, darkest, and middle-est colors, which were pretty jagged. These blend much more pleasantly.
It’s difficult to quantify what the advantage is in adding a 5th ply. Is it just a squidge airier, rounder, smoother? The law of diminishing returns definitely applies.
Especially when you run into the most obvious disadvantage in making 5-ply: I only have 5 fingers. Meaning I only have four spaces between my fingers to hold singles. Which means that plying was a gobbledy-gook mess. I didn’t try very hard, to be honest, which is absolutely my own fault, but it’ll make me think twice before trying again.
Still, it made a happy, squishy yarn, and now I can say I’ve made a 5-ply!
More details of yarn are raveled here.