I, personally have never used anything but 100% cotton, even for charity quilts. The results of 100% cotton go together beautifully, look professional, and can be washed by the recipient. People used to give me a lot of fabric, and I spent many hours on my livingroom floor sorting usable and unusable. One tip: Sometimes you just can't tell whether a piece of fabric is cotton, polyester, or a combination. Go to your sink, cut off a small corner and set it on fire. If there's any polyester in it the burned corner will be melted and hard. If 100% cotton the result will be soft ash.