Flexible, highly transparent and iridescent all-cellulose hybrid nanopaper with enhanced mechanical strength and writable surface

•A novel all-cellulose hybrid nanopaper based on CNWs and CNFs was prepared.•The hybrid noanopaper is flexible, highly transparent, and iridescent.•The tensile strength of hybrid nanopaper was remarkably improved by 76% with 1wt% CNFs.•The hybrid nanopaper is expected to fabricate writable electronic devices. With the development of flexible electronic devices, there is increasing requirement for the inexpensive and environmental-friendly substrates. Cellulose paper has gained great attention because of its abundance, biodegradability and renewability. In this paper, we designed a hybrid nanopaper by introducing native cellulose nanofibrils (CNFs) into cellulose nanowhiskers (CNWs) matrix, which achieved a high optical transmittance while retaining iridescence under polarizing film. This nanopaper is less expensive than neat CNFs-based nanopaper and more feasible for large-scale production. Besides, our transparent hybrid nanopaper possesses the writable surface like regular paper. Compared with commercial paper, however, hybrid nanopaper shows superior optical properties and low surface roughness. The combination of these characteristics makes this nanopaper an excellent candidate for substrates of flexible electronic devices.