Single-wall carbon nanotubes with polyiodide chains inside are interesting from two points of view. According to predictions, first, the iodine structure type inside the nanotube is determined by the nanotube geometry. Second, after iodination all nanotubes become metallic. In this work, we made an attempt to check both predictions. To study the diameter-dependent properties we have taken for a gas-phase iodination the pristine single-wall carbon nanotubes grown by three different techniques providing a different average diameter: a chemical vapor deposition with a Co/Mo catalyst (CoMoCat) with a diameter range (0.6–1.3) nm, a high-pressure CO decomposition (HiPCO) – a diameter range (0.8–1.5) nm, and an aerosol technique with Fe catalyst – a diameter range (1.3–2.0) nm. The Raman spectra have shown a complication of the polyiodide chain structure while the nanotube diameter increased. The optical spectroscopy data (a suppression of E11 band in the UV–Vis–NIR absorption spectrum) have confirmed the theoretical prediction about transformation of all nanotubes into metallic phase after doping.