ASTM D6988 Standard Guide for Determination of Thickness of Plastic Film Test Specimens

Get the Certified ASTM D6988 Guide for Plastic Materials

The professional ASTM D6988 guide helps technicians obtain reliable film-thickness measurements for physical-property testing. Technicians carefully position the film, use suitable precision measurement equipment, take measurements at the required locations, and record the results in the appropriate units. Accurate thickness measurements help analysts calculate properties that depend directly on specimen dimensions. Consistent measurement technique also reduces variation caused by operator handling, instrument characteristics, specimen deformation, and differences in measurement locations. ASTM D6988 serves as a guide rather than a replacement for practical commercial thickness measurements. ASTM specifically notes that measurements obtained using this guide may not agree exactly with measurements made using portable commercial tools.

• Material type: Plastic films and thin plastic sheeting.
• Nominal film thickness: No greater than 0.25 mm (0.010 in.) under the ASTM D883 definition referenced by the guide.
• Property measured: Film thickness.
• Purpose: Provides precise thickness dimensions for calculations of physical properties.
• Measurement approach: Provides recommended practices for obtaining accurate thickness measurements.
• Alternative methods: Allows alternative measurement procedures when they achieve the required measurement precision.
• Units: Uses SI units as the standard measurement system.
• Exclusions: Does not address sampling techniques for obtaining film specimens.
• Commercial classification: Does not address thickness measurements used to classify commercial products.
• Routine quality control: Does not address film-thickness measurement specifically for quality-control purposes.

What are the uses of the ASTM D6988 guide?

ASTM D6988 helps technicians establish accurate film thickness when the thickness value directly affects calculations from another physical-property test. The guide therefore supports consistent specimen characterization across different plastic-film testing programs. Technicians can use the thickness measurements to calculate physical properties that depend on specimen dimensions. The guide also provides a common measurement approach when precise specimen dimensions matter. Common uses include:

• Specimen dimensional measurement: Determine accurate plastic-film thickness before physical-property testing.
• Physical-property calculations: Provide thickness values required for calculations expressed in physical units.
• Plastic-film characterization: Document specimen thickness before conducting additional tests.
• Test-result consistency: Improve consistency when different technicians measure film specimens.
• Research and development: Establish specimen dimensions during plastic-film development.
• Material comparison: Provide controlled thickness measurements when analysts compare film specimens.
• Test reporting: Supply thickness data for test reports when the applicable test method requires it.
• Alternative measurement verification: Evaluate alternative thickness-measurement approaches against the required precision.

Which Materials Can Be Tested According to ASTM D6988?

ASTM D6988 applies to plastic films for which technicians need thickness measurements as part of determining physical test properties. ASTM’s definition of film referenced by the guide covers sheeting with a nominal thickness of no greater than 0.25 mm (0.010 in.). The guide can support thickness measurements for:

• Thermoplastic films
• Polyolefin films
• Polyethylene films
• Polypropylene films
• Plastic packaging films
• Laboratory plastic-film test specimens
• Other plastic films that fall within the guide’s applicability

Why is ASTM D6988 guide Important?

Film thickness directly affects calculations for many physical properties. Even small thickness-measurement differences can influence calculated values when technicians use thickness in the denominator or otherwise incorporate it into the property calculation. ASTM D6988 therefore provides recommendations for obtaining precise specimen dimensions. It emphasizes that the guide supports precise measurements needed for physical-property calculations but does not replace practical thickness measurements made with commercial portable instruments. Consistent measurement also allows analysts to compare specimens more reliably when thickness varies across a film or between different samples.

ASTM D6988 Testing Process and Data Collection

The technician first identifies the plastic-film specimen and determines which physical-property test will use the thickness measurement. The technician checks the relevant test method, material specification, etc., to ascertain if it specifies particular thickness measurement parameters. The technician formulates the film so as to avoid measurement distortion from folds, wrinkles, dirt, etc. The technician checks the measuring instrument and tests its accuracy. The technician measures the film at the required locations and records each thickness value. The technician should maintain consistent positioning and measurement technique throughout the test. The analyst reviews the recorded values and calculates or selects the thickness value required by the applicable physical-property procedure. The analyst then incorporates the thickness into the relevant physical-property calculation.

Common Challenges and Troubleshooting

Thin plastic film can deform during handling or measurement. Technicians should handle the specimen carefully and use a measurement approach that does not introduce unacceptable deformation. A wrinkle can produce a locally abnormal thickness reading. Technicians should flatten the specimen appropriately without stretching it.  Contact instruments can produce different readings when technicians apply different measurement forces. Technicians should maintain a consistent technique and use equipment appropriate for thin films. An improperly calibrated instrument can introduce systematic measurement error. Technicians should verify the instrument before testing and maintain appropriate calibration records.

Analysis Results and Interpretation

ASTM D6988 produces a plastic-film thickness measurement, normally reported in mm or μm under the SI system. The analyst uses this thickness directly when the applicable physical-property test requires a specimen dimension for its calculation. ASTM identifies precise dimensional measurement as the primary purpose of the guide.

• The technician records the specimen identification, measurement instrument, individual thickness readings, measurement locations, units, and relevant observations. The analyst documents the thickness value used in the associated physical-property calculation.
• The final report contains the specimen identification, the applicable test method, the measured thickness, the units of measurement, the number or location of readings where applicable, and the obtained or selected measure number for further testing.
• ASTM D6988 is a guide, so any material- or test-method-specific parameters shall be reported that impact the measurement. Other measurement techniques may be used provided they meet the necessary accuracy of measurement. Alternative measurement techniques may be used when they satisfy the required measurement precision.
• ASTM does not intend D6988 to replace practical commercial thickness measurements or establish commercial product classifications. Analysts should therefore interpret D6988 results according to the purpose of the associated physical-property test rather than treating the measurement as a universal commercial thickness specification.

Link to ASTM D6988