Abstract
The importance of determining not only the nominal permeability of papers, but also the nature of the flow resistance was confirmed, for cigarette wrapper and for papers used in constructing ventilated filters. For perforated papers, for which the flow is not proportional to pressure drop, it was shown that logarithmic plotting and the use of the form V = k (D P)n is satisfactory and convenient. In applying this principle to ventilated filters it was found that limited, but significant, lateral flow occurs between the tipping and porous plug wrap papers, although the flow does not extend over the entire unglued area. With the use of small perforations and extremely porous plug wrap paper, the resistance of the plug wrap paper plays a very minor part in controlling dilution flow.