I've not noticed a difference, but then I rarely prewash unless a fabric doesn't pass the "white paper" test--where you rub white notepaper on the deep color and if no color on the paper = no wash. that leaves the sizing in and keeps the fraying to a minimum. Yes it might shrink--but most quilt shrinkage is going to happen because the batting shrinks usually anywhere from 3-5% (crinkley look). I'm trying to break the steam habit and use Best Press or starch instead.