Introduction

The ASTM D3985 standard is a widely recognized test method for determining the oxygen gas transmission rate (OTR) 

through plastic films and sheeting using a coulometric sensor. This method is essential for industries that require 

precise measurement of oxygen permeability, such as food packaging, pharmaceuticals, and medical device packaging, 

where oxygen exposure can significantly affect product quality and shelf life.

Scope and Application

ASTM D3985 measures the steady-state rate at which oxygen gas permeates through a flat plastic film or sheeting 

under specific conditions of temperature and humidity. The test is applicable to materials with OTR values ranging

 from 0.05 to 200,000 cc/(m²·day·atm).

Test Principle

The method involves sealing the test specimen between two chambers in a diffusion cell:

Upper chamber – Exposed to a controlled flow of oxygen (O₂).

Lower chamber – Contains a nitrogen (N₂) carrier gas that transports permeated oxygen to a coulometric sensor.

The coulometric detector measures the amount of oxygen that passes through the film by generating an electrical 

current proportional to the oxygen concentration. The OTR is then calculated based on the measured current, film

 area, and oxygen partial pressure difference.

Testing instrument：OTR-D3 Oxygen Permeability Tester

Advantages of ASTM D3985

High Sensitivity – Coulometric sensors provide accurate detection even at very low transmission rates.

Wide Measurement Range – Suitable for both high-barrier and permeable materials.

Standardized Methodology – Ensures repeatability and comparability across labs.

Comparison with Other Methods

Unlike ASTM F1927 (which uses a colorimetric detector for oxygen transmission) or ASTM D1434 (for gas permeability

 of rigid plastics), ASTM D3985 is optimized for flexible films and provides highly precise OTR measurements.

Conclusion

ASTM D3985 is a critical standard for evaluating the oxygen barrier properties of plastic films, ensuring that packaging materials meet performance requirements. By using a coulometric sensor, this method delivers reliable and reproducible results, making it indispensable for industries where oxygen sensitivity is a concern.

For accurate testing, proper calibration, controlled environmental conditions, and adherence to standard protocols are essential. Manufacturers and researchers rely on ASTM D3985 to develop packaging solutions that extend product shelf life and maintain quality.