I think that the amount of quilting also affects the wrinkling. If it's only lightly quilted there will be more wrinkling, in my experience. I iron it to get the wrinkles out on quilts where I don't want wrinkles (a lighter iron setting for polyester batting, as someone already said). I think that cotton thread is preshrunk and doesn't shrink more. Polyester thread quilts beautifully, also.