A commonly used exit window material for x-ray lithography beamlines is beryllium, which combines a high degree of transparency to x rays with photon energies greater than 1000 eV, with the material strength that allows the use of thin windows that can support atmospheric pressure. The mechanical and x-ray transmission properties of beryllium foils are dependent on the purity of the initial materials and the fabrication technique used in the foil formation. An evaluation of the strength and x-ray transmission of foils prepared by using different initial materials and different techniques is presented. Improvements in exposure uniformity that are obtained by scanning to average the x-ray transmission variations are discussed.