Measurement of Paper Porosity

The ''porosity'' or ''air permeability'' of cigarette tissue is measured by many different instruments, is expressed in various units and it is frequently impossible to correlate such measurements and the readings of such instruments. The property of a paper whereby it allows air and gases to pass through it while still containing the burning tobacco rod is of great and increasing interest in both the Research Laboratory and Raw Material Control Laboratory of the cigarette and filter rod manufacturer. Interest in papers of higher air permeability continues to grow, particularly in regard to the so-called ''Health Hazards of Smoking", and thus the effect of smoke dilution. Such interest by the cigarette and filter rod manufacturer necessarily means that the paper manufacturer must pay especial attention to this property during paper manufacture and in development work. He also requires to define and measure the property in his control and research laboratories. Unfortunately, there is no common language to describe this property and as interest in higher porosities grows so the shortcomings of some methods of measurement are highlighted. The situation is further complicated by the need of control laboratories for robust, simple to operate instruments, while a research laboratory might be more interested in accuracy and precision, while being less affected by the demands of careful operation and manipulation. Likely sample sizes can also vary, from small spills cut from individual cigarettes or rods, through long narrow skeins to the papermakers' sheets. A standard definition of air permeability of a sheet of paper has therefore been proposed and an instrument has been designed, using this definition, to meet the requirements of all interested parties. A number of these instruments have been built and proved by practical usage