Easy cover ii saves you time and money by turning your paperbacks into hardbacks. Tests show that using easy cover ii will extend the circulation life of your paperbacks by more than five times. Rigid cover with flexible spine prevents damage. 15 Mil clear polyester front and back covers 2 mil wrap-around spine ph. neutral, non-yellowing permanent adhesive wipes clean we recommend 2 strips of kapco's easy bind tape to reinforce your books binding to make them last even longer!