Abstract VARIOUS means which have been suggested for the preparation of thin films of rubber and similar materials include their deposition on glass, porcelain, sheet metal, and mercury. The use of rigid surfaces is open to the objection that in the case of some materials the adhesion of the film may be troublesome. The removal from such surfaces, of films of materials which are subject to permanent deformation on stretching, tends to lessen the uniformity of their thickness. In connection with the study of the permeability to gases of thin films unsupported by fabric, a satisfactory and simple method was found for their preparation.