Abstract: Monolayer films with high permeability, being thin and light, are very promising to be new absorbers used in mordern electronic systems. It has been conventionally thought that single-layer absorbers with the thickness to be/4 have the most efficient absorption. While this presentation demonstrates analytically that the thicknesses of high-permeability thin films, which have the best absorption at fixed frequencies, are less than λ/4. It also shows that the permeability of films has great impact on the bandwidth of absorption.