A composite includes a plastic substrate and an electrical insulator layer formed on the plastic substrate. The electrical insulator layer contains boron nitride nanotubes (BNNTs), which may be unmodified or modified BNNTS. The composite is suitable for use in making printed electronic devices. A process includes providing a plastic substrate and forming on at least a portion of a surface of the plastic substrate a layer that contains the BNNTs. A metallic ink trace is formed on a portion of the layer, such that the metallic ink trace is spaced-apart from the substrate. Using photonic or thermal sintering techniques, the metallic ink trace is then sintered.