What is the brand? You can find out shrinkage rates by going to the manufacturer's website. I usually just Google the brand name and type of batting to find the specific manufacturer's page with the info I want.
Is it Warm and Natural you are looking at? This is needlepunched through scrim and shrinks similar to 80/20 battings. The scrim makes it more stable than 80/20, but also results in a flatter quilt than 80/20.