The need of light weight constructions and parts with tailored or even more homogeneous mechanical properties especially for structural components leads to the use of alternative forming technologies. These forming processes like sheet metal hydroforming are established to gain more flexibility and to increase the forming limits. But to apply this forming technology successfully, it is necessary to overcome some obstacles. One typical challenge for hydroforming of blanks, which has prevented further application of this technology, is the sealing of the cavity in the flange area. Nowadays there are a lot of basic approaches to accomplish a sealing in this tool area. Commonly a sealing can be reached by increasing the contact pressure in the outer region of the blank. This approach reduces the possible blank draw in and hence abates the possible realisation of complex part geometries. One possible approach to increase the ratio between cavity pressure and contact pressure in the flange area is the choice of a capable active fluid medium. The aim is to reduce the contact pressure in the flange area and nevertheless ensure a complete sealing. In this case the magnetorheological fluid (MR-fluid) BASF Basonetic 5030 is used as a pressure medium for hydroforming. For characterizing this fluid under different amounts of magnetic flux density and in comparison to a common hydraulic medium, an experimental setup was built up to gain process relevant data for hydroforming processes. Therefore different experiments were carried out with different media and different flux densities for the MR-fluid. To get more information about the mode of action and the accessible amounts of cavity pressure and related contact pressures in the flange area, these two process parameters were varied.