The TD-prompt component in the TOF distributions of Ar atoms that scatter from FiberForm arises from the three-dimensional network of carbon fibers, which presumably causes multiple bounces of the incoming atoms on different surfaces of the individual carbon fibers and drives them toward thermal equilibrium through inelastic energy transfer on each bounce. Such thermal scattering dynamics was not observed in our earlier similar studies of hyperthermal Ar atoms scattering on the two-dimensional surfaces of vitreous carbon and HOPG , where we observed only non-thermal scattering with angular distributions that were lobular and peaked far away from the surface normal. The lobular angular distribution of scattered Ar from vitreous carbon was slightly broader than that from HOPG, presumably because the surface of vitreous carbon is rougher than the HOPG surface. An individual fiber that is rougher, on an atomic scale, than the surface of vitreous carbon would be expected to promote randomization of the scattering angle distribution and result in a localized angular distribution that is relatively broad, but it would not lead to a significant TD-prompt component following impact by highly energetic incident Ar atoms. Studies of Ar scattering from liquid hydrocarbons (squalane and PFPE), which are very rough on an atomic scale, showed that the TD-prompt fraction in the TOF distributions was only ~30%. By contrast, the percentage of TD-prompt Ar flux was ~50% from FiberForm, indicating that the TD-prompt component arises from multiple bounces of Ar and not from the roughness of individual fibers.