“…Extreme nanowires and encapsulated nanomaterials have recently garnered significant interest, particularly in relation to the use of very narrow single-walled carbon nanotubes (SWCNTs) as confining templates. − The resulting encapsulation engenders modification to the properties of the host SWCNTs but also profound alteration of the properties of the embedded nanowires, as a consequence of nanostructuring imposed by the latter. The van der Waals forces at the internal surfaces of the SWCNTs constrain the encapsulated material to cross sections as small as ≃1 nm 2 , resulting in structures that are completely different to the bulk form of the material, , producing unprecedented new nanostructured crystalline forms. These can be observed experimentally but also anticipated by predictive modeling methods including molecular dynamics (MD), − density functional theory (DFT), , and ab initio random structure searching (AIRSS). − Both experimentation and theoretical modeling are making significant headway in terms of measuring and predicting new functionality of novel nanostructured crystalline forms including modified phonon optics, anticipated band gap modification but, most recently, potentiation of thermoelectric properties in the smallest crystalline forms, prompting new studies into similar materials and other phenomena on a similar scale including electrochemical reactivity …”