A method for manufacturing a polymeric inner liner for a storage tank, particularly a hydrogen storage tank, comprising: providing a cylindrical body of polymer material, having a first open end and a first peripheral connection tab at the first open end, the cylindrical body comprising a structural layer and a barrier layer; providing a dome-shaped end cap of polymer material having a base with a cross-section essentially corresponding to a cross-section of the first open end of the cylindrical body and having a second peripheral connection tab at a peripheral end portion of such end cap; placing the end cap with its base onto the first open end of the cylindrical body and with the first and second peripheral tabs in contact with each other; and welding both peripheral connection tabs together. A storage tank made using such liner. Use of such tank for storing hydrogen.