You pretty much need 110 lb or heavier. I bought a pack of 12"x12" cardstock on sale, and although most of the sheets were the heavyweight stuff, for some odd reason the white sheets were slightly lighter. I figured no problem for something small like hand plates. Nope, two tries at pepping them with the lighter cardstock and each time they twisted and warped just during the pep stage - that's without any resin on them yet. The third pep of them with 110 lb cardstock has them holding their shape properly.