If you like a thinner purse, you can use something lighter. If you like a super thin purse you could use nothing. Those feel to me like they are flimsy and when you put something in them they look all lumpy. I am going to try a heavier pellon for my next one just to see how it feels. Did you figure out the pocket yet? Lay it on the bag the way you want it and flip it down. Sew the unfinished edge down. (the top should be finished)