AbstractThe diffraction of X-rays by multilayer stearate soap films has been studied as a function of (a) the number of diffracting layers and (b) the bivalent metal present. Both “Y” and “X” type structures have been built and analyzed with Al and C Kα radiation. The measured diffraction efficiency is compared with that predicted theoretically and with that obtained from a single crystal such as potassium acid phthalate.