An epoxy resin is prepared as a robust, flexible, freestanding nanomembrane, with thicknesses as small as 20 nm, and perpendicular dimensions of a few centimeters (see figure, width of membrane 2 cm). The existence of a densely crosslinked structure within an ultrathin matrix is the key element for the strength of the nanomembrane. The membrane thicknesses discussed here are approaching the size of large molecules and molecular assembly units.