Physically Cross-Linked Ultrathin Elastomeric Membranes This work was supported by the Max-Planck Gesellschaft, the Deutsche Forschungsgemeinschaft (project Gö 693/2), and the Kalhof-Rose Stiftung. The experiments were conducted at the Max-Planck-Institut für Kolloid- & Grenzflächenforschung, Berlin. We thank H. Möhwald (MPI-KGF), M. Antonietti (MPI-KGF), M. Möller (Universität Ulm), and J. Rabe (Humboldt Universität Berlin) for support and fruitful discussions.