We present the combined results of a computer simulation and adsorption isotherm investigation of CF4 films on purified HiPco nanotubes. The experimental measurements found two substeps in the adsorption data. The specific surface area of the sample and the coverage dependence of the isosteric heat of adsorption of the films were determined from the measurements. The simulations, conducted for homogeneous bundles of close-ended tubes, also found two substeps in the first layer data: one corresponding to adsorption on the grooves and a second one, at higher pressures, corresponding to adsorption on the outside surface of the tubes. Our computer simulations are in very good agreement with the experimental data.