The cotton batting will shrink just enough to give quilts that wonderful old-fashioned look so many people want when the quilt is washed. Polyester battings do not do this.
Polys are hotter on the body as they trap heat and do not breathe. This is much less an issue with cotton or wool battings.
Both cotton and wool from Hobbs are easier to work with from the package when they are "washed" first before layering. Do this by soaking only -- NO AGITATION! -- in cool water in your washer Spin to drain. Fluff on AIR DRY in the dryer for 10-15 minutes until damp dry.
Jan in VA