I always prewash fabric, any coming into my house, as I sometimes find awesome cottons at yard sales. I did learn a lesson recently from fabric purchased at a big-name store--never buy fabric on which the manufacturer is ashamed to print their name. This fabric, sewn into blocks with good quality fabrics, stretched while sewing. It was for a charity lap robe, so not a big deal, but would have been if a gift or cherished quilt pattern.