I'm testing how to weave a felted yoga mat bag. I warped the loom with Harrisville Designs worsted-weight yarn in a lilac shade at 8 ends per inch. The pattern is set up for Balanced Twill from Davison, but I'm weaving the fabric in plain weave because I found the samples that I did in twill to be too busy. The warp is the same lilac, a deep violet, and a sea-glass green and is woven at about 4 picks per inch.
The result is a very open fabric, more like a large-scale burlap than a woven cloth. But I found through sampling that felting is counter-intuitive: the more open and floppy the fabric, the more dense and thick is the final felted product. And I did decide to just jump into the project after forcing myself to do two different sample warps. Either it will work, or I'll have a piece of felted tweed cloth to find a destination for.
Trying to think ahead to what I would need if I was knitting the bag instead of weaving it, I put in a floating selvage of a mercerized cotton thread, doubled, at either edge. This makes it much easier to keep the margins straight - and will allow me to have a focus for where to pick up stitches or seam when the cloth is felted. (Note: I decided to seam the tube before felting. But the floating selvages still helped keep my edges straight and showed me where to put the needle as I was seaming.) I did something similar at the top and bottom edges, but as I also decided to knit a bottom by picking up stitches from the lower edge, I'm not sure that I needed this step. Next time, I'd use a contrast color in the warp yarn so that when I pick the stitches up for the bottom, I'd have a hem in a different color inside the bag.
This is all in the speculative stage. I'm trying to focus and finish the finishing (still need to pick up and knit on a strap) so that I can toss it all into the washing machine and see what happens.