I haven't worked with the 100% cotton, but I often prewash my Hobbs 80/20, particularly if the fabrics in the top and backing have been prewashed. I put it in a rinse and spin cycle, then toss it in the dryer, and it comes out very nice. When using the batting in quilts where the fabric has not been prewashed I don't want to shrink it, but I do want to get rid of the wrinkles, so I just toss it in the dryer on air fluff for about 15 minutes, and the wrinkles just disappear.