In the application of plastic sheet materials to commercial uses, one of the serious objections which often arises is the impermeability of the material to fluid flow. It is thus desirable to devise a process which permits the control of porosity in sheet materials. Such a process, as a matter of fact, has been developed by the author’s company, and is commercially known as “electroventing.” Electroventing consists of passing electric sparks through the sheet material in such a manner as to produce a desired distribution of holes, and holes of a specified size. The combination of size of holes and number of holes will determine the fluid-flow characteristics of any material. This paper deals specifically with air flow through plastic sheet materials, together with an account of how the porosity may be controlled by electroventing.