The Dive Rite Optima counterlungs have an outer, zippered, Cordura cover that protects the inner bladder. The zipper is easily accessible underwater and makes a great place to store your constant PO2 tables, open circuit bailout tables, flexible skills sheets or last minute checklists. Of course you don’t want to use this area for anything heavy or sharp, but a few sheets of flexible material won’t get in the way at all. IANTD makes a great set of flexible tables and Mark Derrick of Dive Rite Express authored an excellent last minute checklist that can be cut down and laminated. Download it here for free!