Cigarette paper air permeability testing determines the airflow resistance of cigarette paper, plug wrap, and tipping paper, expressed in Coresta Units (CU), and is a decisive parameter controlling burn rate, puff count, dilution, and smoke yields. This technical guide explains the measurement principle, applicable standards such as ISO 2965 and GB/T 23227, sample preparation, instrumentation, and quality control requirements for tobacco industry and accredited third-party laboratories.
Technical Overview
Air permeability is one of the most critical physical properties of cigarette paper, defined as the volume of air passing through a unit area of the material in a given time under a standardized pressure differential of 1.00 kPa. The result is expressed in cubic centimetres per minute per square centimetre (cm/min), commonly referred to as Coresta Units (CU), in reference to the historical scientific cooperation organization of the tobacco research community.
Permeability directly governs how much air is drawn through the paper during a puff, which in turn influences static burn rate, puff count, carbon monoxide and tar deliveries, and overall smoking performance. Conventional cigarette papers typically fall in the range of 10 CU to 100 CU, while highly permeable plug wrap or perforated tipping materials can reach several thousand CU. Precise, repeatable measurement is therefore essential for both paper manufacturers and cigarette producers.
The internationally recognized test method is ISO 2965, which specifies the apparatus, calibration, and procedure for determining the air permeability of cigarette paper, filter plug wrap, and filter joining paper. In China, the product standard GB/T 23227 defines permeability requirements for cigarette paper and adopts the corresponding measurement methodology. Conditioning of specimens is performed according to ISO 187, and calibrated reference apertures traceable to recognized metrology frameworks are used for instrument verification.
Testing Samples
Conventional Cigarette Paper
Standard wrap paper used on the tobacco rod, typically in the range of approximately 20 g/m2 to 30 g/m2 basis weight, containing cellulose fibers and calcium carbonate filler. Permeability values usually range from 10 CU to 100 CU, and uniformity across the web is a key acceptance criterion.
High Permeability Cigarette Paper
Papers engineered with elevated porosity, often achieved through controlled filler content, bursting agents, or electrostatic perforation, designed to increase air dilution and reduce puff counts and smoke yields.
Banded Reduced Ignition Propensity Paper
Cigarette paper carrying narrow bands of low-permeability coating applied to meet fire safety regulations. Band permeability is verified separately because the extinguishing behavior of the cigarette depends on the contrast between band and base paper permeability.
Plug Wrap and Tipping Paper
Plug wrap surrounding the filter and tipping or filter joining paper may be unperforated or perforated by laser, mechanical, or electrostatic means. These materials span a wide permeability range, from low permeability plug wrap below 50 CU to perforated tipping papers of several thousand CU, and are tested to confirm ventilation design targets.
Testing Items
Core measurement and evaluation parameters for cigarette paper air permeability testing include:
- Air permeability in Coresta Units (cm/min) at a pressure differential of 1.00 kPa
- Permeability of individual perforation zones in perforated tipping and plug wrap materials
- Cross-direction and machine-direction permeability profile across the paper web
- Coefficient of variation of permeability as an indicator of uniformity
- Band versus base paper permeability contrast for reduced ignition propensity grades
- Supplementary flow characterization at reduced pressure differentials for highly permeable or perforated materials where flow behavior deviates from laminar conditions
Testing Methods
Principle
A circular specimen of the paper is clamped in a sealed measuring head with a defined test area, typically 2.00 cm2. A stable pressure differential of 1.00 kPa is established across the specimen, and the volumetric flow rate of air passing through the paper is measured. The permeability is calculated as the flow rate per unit test area and reported in Coresta Units.
Apparatus and Calibration
Testing is performed with an electronic air permeability tester equipped with a precision clamping head, pressure regulation and sensing elements, and a flow measurement system. Instruments are calibrated using certified reference apertures or calibrated flow devices traceable to national metrology standards. Corrections for ambient air density and viscosity may be applied when calibration and testing conditions differ. Regular verification with working reference samples is required between calibrations.
Sample Preparation and Conditioning
Specimens are cut from the sample roll or sheet free from wrinkles, pinholes, creases, and visible defects, and are marked to record their position relative to the machine direction. Prior to testing, specimens are conditioned in a standard atmosphere of (23 ± 1) °C and (50 ± 2) % relative humidity in accordance with ISO 187 until equilibrium is reached. Testing is carried out in the same atmosphere.
Procedure
- Verify instrument calibration and zero setting before the test sequence begins.
- Clamp the conditioned specimen securely in the measuring head, ensuring a leak-free seal without damaging the test area.
- Apply the standardized pressure differential of 1.00 kPa and allow the reading to stabilize.
- Record the permeability value in Coresta Units, ensuring the reading is within the calibrated range of the instrument.
- Repeat the measurement on at least ten specimens distributed across the width of the sample.
- Calculate the mean value, standard deviation, and coefficient of variation, and report results together with the test area, pressure differential, and conditioning atmosphere.
Repeatability and reproducibility limits are defined in ISO 2965 and should be confirmed in laboratory quality control records. For perforated materials, measurements are positioned so that the perforation pattern is fully and reproducibly contained within the test area.
Applications
Cigarette paper air permeability testing supports multiple technical and regulatory objectives across the tobacco supply chain:
- Cigarette design and ventilation engineering, where paper and plug wrap permeability determine dilution levels and filter ventilation efficiency
- Control of puff count, static burn rate, and deliveries of tar, nicotine, and carbon monoxide measured on smoking machines
- Verification of reduced ignition propensity banded papers against fire safety regulations
- In-process and release quality control at paper mills, including web profile monitoring
- Incoming inspection and supplier qualification by cigarette manufacturers
- Independent verification of conformity by accredited third-party laboratories
FAQ
What is a Coresta Unit?
A Coresta Unit (CU) is the air flow in cubic centimetres per minute passing through one square centimetre of paper under a pressure differential of 1.00 kPa. It is the industry-standard reporting unit for cigarette paper permeability under ISO 2965.
Why is the pressure differential set at 1.00 kPa?
The 1.00 kPa differential provides a reproducible reference condition that approximates the pressure drop across cigarette paper during puffing while remaining stable and easy to control in laboratory instrumentation. It allows consistent comparison of results between laboratories and suppliers.
Which standards govern cigarette paper air permeability testing?
ISO 2965 specifies the determination of air permeability for cigarette paper, plug wrap, and filter joining paper, while GB/T 23227 defines corresponding product requirements in the Chinese national framework. Specimen conditioning follows ISO 187.
How many specimens should be tested?
A minimum of ten specimens is recommended, taken from positions distributed across the paper width. Reporting the mean together with the coefficient of variation provides a reliable indication of both permeability level and uniformity.
How is perforated tipping paper tested differently?
Perforated materials are measured with the perforation pattern fully contained within the clamped test area so the result reflects the effective ventilation contribution of the paper. Because flow through perforations may not be purely laminar, some evaluation programs additionally record flow behavior at other pressure differentials to characterize the material more completely.
What factors can affect test accuracy?
Key influences include instrument calibration and leak-tightness of the clamping seal, ambient temperature and humidity, specimen defects, and correct positioning of perforations. Controlled conditioning, calibrated reference apertures, and trained operators in accredited laboratories minimize measurement uncertainty.
