While I was warping (10 yards!) for the first time on a new loom, I realized that I couldn't use the cardboard separators that we use in between layers on the back beam of our first loom. Instead of using a paper bag, I decided to use FREEZER PAPER. I just laid the box of freezer paper on the floor below the back beam with the edge started, making sure it was very straight. As I started rolling the warp on, the freezer paper just came straight out and made it the easiest beaming we ever did. The only downside is that the freezer paper is only 18" wide, so it wouldn't work so great for wider widths.