AbstractMicrobeam XRF measurements of polymer foils of different thickness were performed to compare the homogeneity of the distributions of element admixtures in plastics (polycarbonate foils). The measurements were performed with an energy‐dispersive x‐ray fluorescence spectrometer utilizing capillary optics. The spatial resolution of the spectrometer set‐up was about 30 µm. The distributions of Ti, Cr, Fe, Sr and Ba were investigated. The samples were prepared from plastic foils having different thickness ranging from about 90 to 2600 µm. For each sample, line scan measurements were carried out, each line scan consisting of 128 points. The local concentrations of elements along the scanned path were calculated using the modified backscatter fundamental parameter method. The influence of the foil thickness on the element distributions obtained was observed. It was found that of the investigated elements, barium had the most uneven distribution. Copyright © 2001 John Wiley & Sons, Ltd.