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Sunday, July 14, 2013

Coresta Porosity for Cigarette Paper

Coresta stands for Centre de Cooperation pour les Recherches Scientifiques Relatives au Tabac. Coresta is an international organization of representatives from the tobacco industry, sharing scientific/technical information relating to the tobacco plant as well as tobacco products.

The Coresta method for porosity is commonly used in the cigarette industry.  The test pressure approximates the pressure differential that cigarette paper is subjected to in its actual use.  Coresta air permeability is the flow of air (cubic centimeters per minute) passing through 1 square centimeter surface on the test piece at a measuring pressure of 1.00 kPa.  The actual test area is as large as 10 square centimeters, but the results are normalized to flow per square centimeter.  Since the product tested is frequently supplied on narrow width “bobbins”, the measuring head is commonly manufactured in an oblong geometry in order to achieve a relatively large test area on the narrow strip.  Due to the frequent occurrence of pinholes in these grades, it is important to test at the specified Coresta pressure, and to generally test a 10 square centimeter area in order to obtain the desired standard deviation.  When the test area is reduced, pinholes will cause a higher standard deviation, as such pinholes would represent a larger percentage of the test area.  There are procedures used to test cigarette paper at different pressures in order to assess the effect of pinholes on airflow.  The flow comparisons show larger deviations from laminar flow when pinholes are tested. 

This method is commonly used throughout the tobacco industry around the world.