In this scientific work on hand two apparently similar types of liquid silicone rubber (LSR) for membrane applications were being characterized mechanically and compared. For a first, basic characterization of the uncured materials, Shore A hardness, uniaxial tensile and compression tests were performed. Using an adapted proposition, a friction-free stress-strain diagram was evaluated for the compression behaviour. A one-camera experimental set-up in combination with bubble inflation tests was used to analyse equi-biaxial data. Based on the mechanical tests hyperelastic material laws were determined using a fitting procedure in a finite element code. For both materials a short-term postcuring at high temperatures was assessed with the aim of stabilizing their mechanical properties. The effects of an additional thermal curing at 90° C over a time period of 3000 hours were investigated. The results of both the mechanical haracterization and the thermal curing showed a significant difference between either materials selected.