I have been hand spinning classic gansey yarn from traditional British long wool fleece. The extreme fineness of the singles that I had to spin to get the right grist on the final yarn was a real eye opener.
Yes, I had deconstructed modern commercial gansey yarns and had seen how fine the plies in it were. That is what triggered my decision to learn to spin. However, there is a big difference between seeing such fine singles (as a non-spinner) and actually spinning such singles as a (beginning) spinner. Moreover, spinning gives one time to think.
One thinks of England as a cool place, full of sheep and wool, so wool must be cheap and they can afford to be extravagant with wool in their clothes, right? England was full of wool because wool was useful and valuable. In fact, the English were very good a making a little bit of wool provide a lot of warmth. It is only recently, that they have become extravagant with their wool.
The English have long traditions of spinning very fine and knitting with fine needles. The result is fabrics that by modern standards of hand knitting are extraordinarily warm, but by modern standards of hand knitting are light weight and have very little bulk. They really are nice fabrics for all kinds of uses, because they are so much warmer than we expect such a thin fabric to be.
I spun the singles to be plied into the gansey yarn, and I wondered, what would happen if I plied these up into a 2-ply yarn? Knit on fine needles (UK 16 / 1.6 mm) I got a fabric warm enough for cool mornings in spring-summer- fall. I made up some 3-ply, knit it on 1.75 mm needles, and lo and behold! I got a fabric that is warmer than modern commercial gansey 5-ply yarn knit on 2.5 mm needles! In a mild climate, 3-ply (22 wpi) on #00 needles was/is good for winter wear. (For skiing, I might put on long pants.) Again this is a stealth fabric. Look at the fine 3-ply knit on the #00 needles next to the 5-ply knit on the larger needles and you would say that the gansey fabric is many times warmer. However, it is not.
This brings home several lessons. The first is that fine yarns can produce very warm fabrics. The second is that gansey 5-ply yarn knit on “big” needles does not produce a very warm fabric. The third is that appearances can be deceiving and you need to test a fabric for warmth, because the eye can be deceived. The fifth is that you do not need a bulky fabric to be warm under most conditions. The sixth is that 5-ply gansey yarn knit tightly produces a fabric that is suitable for very cold conditions.
Fisherman’s sweaters in the modern context are knit loosely because most people do not want that kind of warmth.