I went and read the suzyquilts explanation. My experience with Warm & Natural was totally reversed. I put this note in my phone because of a really bad tufting problem, otherwise known as bearding, that occurred on one of my quilts that I quilted on my long arm.
This is what I go by!
This particularly applies to W&N - The smooth with very little surface definition or texture lays against the wrong side of the backing fabric. The Scrim which has bumpy, needling holes visible with specks of seeds or stems goes to the back side of the pieced quilt top. If you put this batting in backwards, it pulls little tufts out of all the needle holes on the top, and you cannot get rid of them.
In retrospect, I really should have ripped all that quilting out and redid the quilt. I still have that one because I am not going to be giving it to anyone in it's condition.