I, too, have used the center from bedskirts as foundation fabric for crumb or string blocks. I also use used dryer sheets as foundations. The drawback for dryer sheets is that they are not that big. The largest block that I've been able to get from them is 6 inches square. Finished blocks will be only 5 1/2 inches square, due to the seam allowance, but I just finished a string quilt (throw size) using the 6 inch dryer sheet foundations.