Sometimes you can tell from the weave...it's usually flatter on the back and more dimentional on the front...but like everyone said, if you can't tell, others probably can't either. If I think the difference will be noticeable, I mark the backside with chalk. Of course, the smart thing would be to do this before cutting, but sometimes I forget. I just finished one that I didn't even attempt to decide which side was up and it looks great. I can probably be less fussy about it than I am.