Thin layers with high barrier to oxygen and other gases/vapors are a key component to a variety of applications, such as flexible electronics, food and pharmaceutical packaging. Vapor deposited thin films, such as SiOx, provide significant barrier, but are prone to cracking when flexed, require special (i.e., non-ambient) processing environments (e.g., vacuum), and can involve complex fabrication when layered with polymers. We are developing transparent, metal-free, multilayer thin films (less than one micron thick), deposited using layer-by-layer assembly, with polymers and/or nanoplatelets that have oxygen permeability below SiOx and very similar to metallization. Furthermore, some of these unique films exhibit carbon dioxide/hydrogen selectivity that exceeds any mixed matrix membrane currently available. All of these films are deposited quickly from water-based solutions, making this a very industrially relevant technology. More recently, we are also engineering multilayer thin films capable that exhibit a unique combination of low gas permeability and ability to experience large strain (> 15%) without any damage.