Self-adhesive gaskets materials are sheets for gaskets which are covered with an adhesive backing designed to help at the fitting stage. The adhesive also helps to reduce the chance of a gasket losing its shape.
Generally, the gasket will have paper covering the adhesive and it will be peeled off just before the gasket is fitted to the designated surface. The adhesive is only for aiding the fitting of the gasket and does not play any sealing or structural role.