Boy, John, you are so right about those bags that the grocery stores sell. I have repaired some of them several times and my husband always complains about them not staying open when he is trying to fill them. You've got a good idea going there about using the twill for stiffness. I have some upholstery fabric that was given to me and I think that would work well too. I also saw on-line the idea of making bags from dog food and bird seed bags. Very inexpensive to make. They are pretty sturdy and can be attractive if you make sure you keep the photo of the dog or birds in the center of the bag. However, I would think that maybe they aren't as pliable??? I am going to try one with our birdseed bag. Hope it works. Your bags are very attractive.