Films of single-walled carbon nanotubes are promising for various electro-optical applications. Their engineering at the nanoscale requires a robust method of the contactless, non-invasive determination of structural properties. Here we present a study that uses specular reflectometry for this purpose, namely to determine the film thickness. Analysis of the reflection coefficient of neutrons, as well as X-rays, makes it possible to obtain a normal density profile and thereby trace the effect of densification of films of single-walled carbon nanotubes by ethanol drop casting. The paper summarizes the first experience of using combined neutron and X-ray approach in relation to low-density carbon films. Further steps for the development of the technique are discussed.