Hobbs 80/20 doesn't have scrim. Some other Hobbs products do, as does W&N. The preference for scrim side down is for longarm and domestic machine use, but 9 times out of 10 (I just made that figure up) you won't have a problem if you get it wrong. But if you do discover a problem after the quilt is finished, it's too late to fix it. (Unless you enjoy picking all those stitches out of the quilt.)