A room temperature colloidal method for coating carbon nanotubes with silicon oxide is described. For the first time, the morphology, chemical composition and SiOx/C interfaces of the coatings were investigated using state-of-the-art transmission electron microscopy and highly spatially resolved electron energy-loss spectroscopy. The amorphous SiOx coatings are < 10 nm thick. Electron energy-loss fine structure analyses indicate that the SiOx is partly substoichiometric. In addition, coatings were also created by a high-temperature route. However, they tend to be more unstable and defoliate when compared to coatings deposited at room temperature.