The transmittance properties of a thin-film are functions of gauge thickness, density and mass attenuation coefficients of the constituent chemical elements. The Analyte-Line Transmittance chart as shown below may help in selecting the correct thin film for a given sample of analytical interest.

Simply refer to the spectral line of the element in the sample having the lowest energy, KeV, or the longest wavelength, Å. Then choose a curve with the highest percentage of transmittance. Finally use the legend to determine which material and thickness.

Considering the transmittance properties is only important for the low atomic number elements.