NOVELTY - The double-sided, carrier-based or unsupported self-adhesive tape useful as a sealing element in fuel cells, comprises a self-adhesive mass, and a siliconized covering, which is used as an application aid in the manufacturing process of a fuel cell and/or a fuel cell stack. The tape has a creep relaxation factor of 0.6 according to DIN EN 13555 with an initial surface pressure of 20 MPa and a simulated stiffness of 500 kN/mm and is produced by UV-radiation. The self-adhesive mass is a solvent-based, a solvent-free or a water-based system and contains a filling material (5-15 wt.%).    USE - Double-sided, carrier-based or unsupported self-adhesive tape useful as a sealing element in fuel cells and/or fuel cell stacks.    ADVANTAGE - The double-sided, carrier-based or unsupported self-adhesive tape can be economically produced in large quantities with high quality, high strength and high elasticity thus reducing the risk of destruction of sensitive fuel-cell components, increases the efficiency of the fuel cells and enabling economical manufacturing of fuel cells with high throughput without using additional sealing materials.    DETAILED DESCRIPTION - The double-sided, carrier-based or unsupported self-adhesive tape useful as a sealing element in fuel cells, comprises a self-adhesive mass, and a siliconized covering, which is used as an application aid in the manufacturing process of a fuel cell and/or a fuel cell stack. The tape has a creep relaxation factor of 0.6 according to DIN EN 13555 with an initial surface pressure of 20 MPa and a simulated stiffness of 500 kN/mm and is produced by UV-radiation. The self-adhesive mass is a solvent-based, a solvent-free or a water-based system, contains a filling material (5-15 wt.%), and contains a reactive cross-linking portion in a concentration of 0.15-1.8%. The tape contains a diffusion film as polymer-compound or aluminum composite system and a latex- or fluoroelastomer-based carrier material and is applied as a stamped part.