The use of protons in backscattering analysis can be of advantage when detecting low- Z elements in a matrix of high- Z material, due to enhancement of the cross section by nuclear potential scattering. For light elements resonances in the nuclear scattering cross section become important in thin film analysis. The spectrum of backscattered protons shows a peak whose width may not only depend on the film thickness but also on the resonance. Effects of film thickness on the analysis of thin films in the region of the 0.46 MeV and the 1.73 MeV resonance in the elastic backscatter spectrum of protons from carbon are discussed. Values for the elastic scattering cross section for protons on carbon in the range from 0.445 MeV to 2.0 MeV at a laboratory angle of 160° are given.