I am economical with my learning, I only learn what I need to know to weave the next project. So, the seemingly straight-forward difference between a tube and double-width can throw me when I expect one and get the other.
With tubes and double-widths, you weave two layers where the layers never mix or cross over in the middle of the cloth; the only difference being, with a tube the weft goes around and around the cloth uniting the two layers at both edges, whereas with double-width it leaves one side open.
If we call the top layer A and the bottom layer B, for a tube you weave A-B-A-B, and for double-width A-B-B-A. The only thing to remember is if your draft has a direction, say a simple twill, you need to consider the direction you twill progresses on the bottom layer, so you don't get a big V in the middle of the cloth, unless you plan to.
A 2/2 twill in double weave, for example, can be expressed in many different ways, but since I prefer the easiest threading in the first instance, I will go with the one below. To make it easy for me, I left the 5th tie-up a blank. The first four (from the left) creates a 2/2 twill for the top layer A, and the last four (on the right), for the bottom layer B. Notice all top layer A shafts (1, 3, 5, 7) are lifted whenever I'm weaving the bottom layer B.
Once I get the tie ups right, I can change the shape of the cloth just by swapping the treadling order. The top part is a tube, the bottom in double width with the right side open. Because I want the twill to go in one direction in the cloth, the treadling on the bottom B layer, (tie-up 6-9) moves from the right to the left, as opposed to the top A layer, (tie-ups 1-4) from the left to the right. If you are on a foot loom, you may want to swap the tie-up so you can have a straight treadling order. Or not, because this way, you can walk it.
Sue, my tube. Its construction could be a nice neck/collar, but this one is a little stiff and heavy, so I shall ask my mother what she'd like.
Tube sox exchange next Christmas, anyone??