Aggh, Suzy Quilts and the other posts are saying opposite rules, even in my sewing room I found notes to myself about batting and one says bumpy side is bottom, put against backing, the other says bumpy side is right side, put against top.
I use Warm & Natural and Pellon, have been putting bumpy side against backing for years, haven't had a problem with bearding. I do FMQ on all my quilts. But I'm certainly not an expert, maybe I'm doing it wrong and have been lucky?