Used dryer fabric softner sheets. I use snuggle, and you would not believe how much product is left after 1 use, so save several and toss into dryer for a "free" load, then when you have accumulated 10 or 20, soak them in warm water to remove the rest of the product and perfume, then dry flat, press with low heat iron, this is free non woven interfacing lightweight, and I use them for foundation piecing crazy quilt blocks, nice rectangular size and very lightweight. Of course there was a email going around about a year ago for all the other uses for used dryer sheets, and it was extensive.
