Mine are all bare rubber with Sailor 2-in-1 glue on the back (others use Aleene's Tack It Over & Over). This allows them to stick to the cases and/or the blocks. If you use a fun foam pad (or similar) under your project when you stamp, then it won't matter that you don't have foam on the stamp itself - you'll still get a good impression. There are others who use Tack 'n Peel on the blocks so they don't need to have anything on the back of the rubber (glue or tape), and they store the stamps in drawers instead of anything that needs to be upright (like a case or binder). I have all of mine in binders, as outlined in a post on THIS THREAD
(which has a lot of other helpful info for you, too, most likely). My post is #17...
A few other threads on the subject are HERE
. My system is based on Diane's method (see post #21 in the last link). Hope that helps you find something that works for you!