Skin electronics require stretchable conductors that satisfy metallike conductivity, high stretchability, ultrathin thickness, and facile patternability, but achieving these characteristics simultaneously is challenging. We present a float assembly method to fabricate a nanomembrane that meets all these requirements. The method enables a compact assembly of nanomaterials at the water–oil interface and their partial embedment in an ultrathin elastomer membrane, which can distribute the applied strain in the elastomer membrane and thus lead to a high elasticity even with the high loading of the nanomaterials. Furthermore, the structure allows cold welding and bilayer stacking, resulting in high conductivity. These properties are preserved even after high-resolution patterning by using photolithography. A multifunctional epidermal sensor array can be fabricated with the patterned nanomembranes.