I use the plastic canvas in-between the lining and the bottom. However, when I don't have the plastic canvas, I have used cardboard... but when I do I make a sleeve out of the lining fabric and slide the cardboard into it and lay it on top of the lining in the bottom of the bag. That way when the cardboard weakens & bends (and it does) I can replace it... and it can easily be removed to clean the bag. Since Hurricane Irene has closed the nearest Joann's (all my plastic canvas is gone) I've been cutting up and using paperback book cover sleeves called "HardBacks" that I had left over from when I had the bookstore. These are VERY durable and don't bend easily; almost as strong as Lazy Girl Designs Bag-E-Bottoms. Don't know if "HardBacks" are still being manufactured but I do love using them in my handbags!