Number one, make something pretty for the donor. Folks who give a lot of stuff really want to be thanked in some small way, especially if they give a LOT.
Don't ask me how I know this, just take my word for it. And should they run into some nice cottons, you will be the one to get them. To non-sewers, fabric is material and material is fabric, unless it is already made up into clothing, which are separated into wash and dry clean.