I get questions often asking about why a silk/wool blend covered the canvas better than a rayon.
The answer to this question brings up an aspect of threads which we, as stitchers, don’t think about much — loftiness, or loft.
Loft, quite simply, is the amount of air spun into a thread as it is made.
Knitters think about loft, because the more air spun into a yarn, the warmer it will be (the trapped air stays warmer than the surrounding air).
Threads which have lots of loft have a wonderful characteristic in needlework, they expand along the length of the stitches. You can see this for yourself very easily. Make a line of straight stitches four threads or so long using a wool or silk/wool blend. Now make another row of stitches the same length using pearl cotton.
The wool stitches fill up the space and sort of become indistinct from each other. They also sit above the canvas a bit. The pearl cotton stitches remain distinct and you might even see white space between them. The wool has more loft than the cotton and so puffs out a bit where it isn’t compressed by the canvas to fill the space better.
This characteristic of threads, especially of wool and wool blends, is important to remember, especially when you thinking about coverage.
All kinds of threads have a place in needlepoint. But remembering about loft can turn a blah piece into one which looks lovely.