You can preshrink a batting if you do not want a crinkle look. But if you are using a polyester batting there is no shrinkage.
Preshrinking a batting is pretty easy if the batting has a good scrim( thats what holds the cotton fibers in place). I have had the best luck preshrinking Warm and Natural ( or warm and white). It has a great scrim, I soak it over night , once in a while submerging the batting as it likes to float. If I get lazy I wet a towel to use a a weight on top of the batting. After it is fully saturated with water , spin , toss in the dryer, regular cotton temp. Do reposition the batting so it does not tangle lke sheets tend to tangle. Once its dry you are ready to use it.
If you want a crinkle look just use it with out pre treatment. You may want to smooth it , if it was a folded packaged batting, by tossin in the dryer for a few minutes.