I went to the local JoAnn Fabric store yesterday looking for .020" - .021" 100% cotton patching to replace my fast dwindling supply. After looking at and measuring a lot of fabric, I found cotton duck, which is a duplicate of what I'm now using: That's the good news. While I was there, I also measured the pillow ticking, since I need some .018" patches. In short, I found some, but they only had one bolt, and no longer carry the thicker, outdoor variety. That's sort of the bad news. They had thinner ticking, but only red- and blue striped. The worse news is that the .018" blue striped ticking is indistinguishable from the .014" - .015" ticking. The lesson to be learned here is to take a micrometer with you when you shop for patching material, as looks and feel are deceiving. Btw, JoAnn carries a nice selection of 100% cotton denim in case your gun is happiest with that material.
P.S. The above fabric thickness is a compressed reading.