Hi QuiltE:
For a top loader -- put in the piece of batting and fill the tub with hot water. DO NOT let the batting aggitate. Just turn the machine off and let the batting sit in the hot water for 10 or 15 minutes. Move the dial on the washer to spin. Spin it out. Put in the dryer on a hot setting and dry. It always came out just fine. If you aggitate it it will just break apart.
Hope this helps, and I hope someone has an idea of how what I can try.
This is how I preshrink mine. I do a lot of hand quilting and it seems to make Warm and Natural softer and easier to hand quilt when it's been preshrunk.