a closing apparatus for closing preferably bag - type packaging units by compression , which units have regions of differing thickness along the package opening to be closed , such as square bottom bags for instance , in particular made of coated or uncoated paper , paperboard , plastic , film , and / or woven material , which packaging units have at least one suitable sealing surface that is integrated in or applied to the material for permanent bonding to a surface that is adjacent to or opposite and pressed against the material , wherein the closing apparatus has a pressing device with at least one pressure device and at least one counter - pressure device between which the packaging units can be compressed , preferably with the application of heat , in the region of their sealing surface . in order to achieve a uniformly durable closure , the pressure device and the counter - pressure device have zones of different pressure and / or different temperature along the package opening to be closed .