The Physical Test Methods (PTM) Sub-Group is a Sub-Group of the Product Technology Study Group and was established in October 2005 under the name of Monitoring and Maintenance of Physical Test Methods (MMPTM) Sub-Group. It was renamed to its current name in April 2011. The PTM Sub-Group's revised objectives, as listed above, were approved by the Scientific Commission and the Board in June 2018.

​Since its creation the PTM Sub-Group has made substantial progress towards these objectives. It has conducted numerous international collaborative studies, published CORESTA Recommended Methods, CORESTA Guides and Technical Reports.

The PTM Sub-Group usually meets twice per year and the meetings are attended by 15 to 20 participants representing cigarette manufacturers, suppliers of materials and instruments for the cigarette industry, analytical laboratories and research institutions.

Development and Maintenance of CRMs

The PTM Sub-Group developed a method (CRM 90) for the measurement of snus pouch sealing strength and carried out a collaborative study to assess the variability of the method. The CRM and technical report on the collaborative study were both published in March 2019.

In April 2014, CRM 77 on the determination of diffusion capacity was published. This publication finalised a development work of more than four years, which was originally triggered by the need to measure the diffusion capacity of bands on lower ignition propensity cigarette papers. Most of the work was carried out in a separate working group usually meeting in close connection to regular PTM Sub-Group meetings. Within the near future it is planned to revise this method and provide an updated version of the CRM.

In May 2019, the PTM Sub-Group launched work on the development of a CRM from measuring the crush strength of flavour capsules for filters. Flavor capsules have become a common component in the filter of many cigarettes, filter cigarillos and also heated tobacco products, and the force needed to break the flavour capsule is an important quality parameter to be determined.

The following CRMs are in the responsibility of the PTM Sub-Group.

• CRM 06: Determination of Ventilation - Definitions and Measurement Principles
• CRM 16: Lamina Strip Particle Size Determination
• CRM 17: Stem Content of Lamina Strips
• CRM 40: Determination of Air Permeability of Materials used as Cigarette Papers, Filter Plug Wrap and Filter Joining Paper including Materials having an Oriented Permeable Zone
• CRM 41: Determination of the Draw Resistance of Cigarettes and Filter Rods
• CRM 53: Determination of Paper Wrapper Burn Speed (revised Jan 2019)
• CRM 77: Determination of Diffusion Capacity by Measurement of CO₂ Transfer Rate Through Material Used as Cigarette Papers and Cigarette Papers having an Oriented Zone of Reduced Diffusion Capacity
• CRM 90: Determination of Dry and Wet Sealing Strength of Pouches for Smokeless Tobacco and Derivative Products - Definitions and Measurement Principles (revised June 2019)

Development of CORESTA Guides

As a complement to CRMs, CORESTA Guides cover more practical aspects of the measurement of physical parameters of tobacco products and their components and help the users in applying CRMs. Guides are also developed to give an overview over measurement principles and to document best practices.

The last Guide published by the PTM Sub-Group is Guide No. 14 “A User Guideline for the Determination of the Diffusion Capacity (D*) of Cigarette Papers” which was developed and published in connection with CRM 77.

The PTM Sub-Group has published the following Guides:

• Guide No. 04 – A User Guideline for the Measurement of Pressure Drop of Cigarette and Cigarette Filter Rods (revised Jan 2019)
• Guide No. 06 – A User Guideline for the Use of Balances for Cigarettes and Cigarette Related Products
• Guide No. 10 – A User Guideline for the Measurement of Diameter of Cigarettes and Filter Rods
• Guide No. 14 – A User Guide for the Determination of the Diffusion Capacity (D*) of Cigarette Papers

Inter-Laboratory Collaborative Studies

On the one hand inter-laboratory studies are usually carried out during the development of a CRM to determine repeatability and reproducibility of the newly developed method, but on the other hand they are also regularly carried out in the form of a proficiency test to allow laboratories to assess their performance with respect to other laboratories. Particularly for accredited laboratories, participation in such proficiency tests is required.

The PTM Sub-Group generally carries out an annual collaborative study on physical parameters, in which filter rods and cigarettes are measured for weight, diameter, pressure drop and ventilation. These studies are statistically evaluated and the results are made publicly available in form of a Technical Report. In 2019, the PTM Sub-Group is carrying out its 12^th Collaborative Study on Physical Parameters. Usually about 15 to 25 laboratories participate in such a collaborative study.

An additional collaborative study was intiated in 2019 on air permeability. This project replaces and complements air permeability cross-checks, mentioned below, often done on a bilateral basis between paper suppliers and cigarette manufacturers.

Furthermore, a smaller number of PTM Sub-Group members maintain calibration laboratories. In order to assess the performance of their calibration laboratories, inter-laboratory studies are carried out regularly as round robin tests. In these studies calibration standards for pressure drop, air permeability and filter ventilation are circulated between the laboratories for measurement. The results are statistically evaluated and also made publicly available as a Technical Report. As the measurement of calibration standards is a high-precision method, which requires sophisticated equipment and a highly controlled laboratory environment, only a very few laboratories participate in these studies. Also, due the time required for the circulation of the calibration standards, the studies are often not carried out on an annual basis.

Reviewed June 2019