http://tobaccodocuments.org/filters/2028468244-8262.html
PM, Philip Morris; van Duuren, B. "VENTILATION LEVEL OF VENTILATED CIGARETTES DURING HUMAN SMOKING". 26 Feb 1985. Bates: 2028468244-2028468262.
http://tobaccodocuments.org/filters/2028468244-8262.html