Introduction

Plastic films are widely used in packaging, construction, agriculture, and medical applications. Ensuring consistent 

thickness is critical for performance, durability, and compliance with industry standards. ASTM D6988, Standard Guide

 for Determination of Thickness of Plastic Film Test Specimens, provides essential guidelines for accurate thickness 

measurement.

This article explores ASTM D6988’s scope, measurement techniques, equipment requirements, and best practices

 to help manufacturers and quality control professionals achieve reliable results.

Scope of ASTM D6988

ASTM D6988 outlines procedures for measuring the thickness of plastic films, typically ranging from 0.025 mm (1 mil)

 to 6.35 mm (250 mils). The standard applies to both rigid and flexible plastic specimens, ensuring uniformity in testing 

across industries.

Key objectives include:

Defining appropriate measurement techniques

Specifying equipment calibration requirements

Establishing procedures for minimizing measurement errors

Importance of Accurate Thickness Measurement

Film thickness directly impacts:

Mechanical properties (tensile strength, puncture resistance)

Barrier performance (moisture, oxygen permeability)

Optical properties (transparency, haze)

Regulatory compliance (FDA, ISO standards)

Inconsistent thickness can lead to product failure, increased waste, and non-compliance with industry regulations.

Testing instrument：PTT-03 Thickness Tester

Measurement Methods

ASTM D6988 recognizes several techniques, each suited for different applications:

1. Mechanical Micrometers

Principle: Uses a calibrated screw mechanism to apply controlled pressure.

Best for: Rigid or semi-rigid films.

Limitations: May compress soft films, leading to false readings.

2. Non-Contact Optical Profilometers

Principle: Uses light interference or laser displacement sensors.

Best for: Delicate or ultra-thin films.

Limitations: Requires a smooth, reflective surface.

3. Contact Dial Gauges

Principle: Measures displacement via a spring-loaded probe.

Best for: Flexible films with moderate thickness.

Limitations: Susceptible to operator influence.

4. Ultrasonic Thickness Gauges

Principle: Measures time delay of reflected sound waves.

Best for: Multi-layered films.

Limitations: Requires calibration for material-specific sound velocity.

Equipment Calibration & Standardization

To ensure accuracy, ASTM D6988 mandates:

Regular calibration using certified reference standards.

Verification of measurement equipment before each test series.

Environmental controls (temperature, humidity) to minimize material expansion/contraction.

Best Practices for Reliable Measurements

Sample Preparation

Cut specimens cleanly to avoid edge deformation.

Condition films at standard laboratory temperature (23°C ± 2°C) per ASTM D618.

Measurement Protocol

Take multiple readings across the film surface (minimum 5 points).

Avoid folds, wrinkles, or air gaps during testing.

Data Reporting

Record mean thickness, standard deviation, and measurement locations.

Specify the method used (e.g., micrometer, optical).

Conclusion

ASTM D6988 provides a structured approach to plastic film thickness measurement, ensuring consistency across

 industries. By selecting the appropriate method, calibrating equipment, and following best practices, manufacturers 

can maintain product quality and compliance.