I prewash batting only when I don't want it to shrink such as for placemats or table toppers. As you saw, it shrinks. Instructions on preshrinking is on the package. I don't know if you can preshrink all batting. The batting shrinks in the dryer, so soak it without using agitation, then run it through the spin cycle. Then stick in the dryer on low. Dry only until it is just damp. Then take out and spread out to complete the drying process.