What is Outgassing Testing? Key Parameters and Procedures

Understanding Outgassing Behavior

Outgassing is a process in which volatile substances leave the bulk of a material and migrate to its surface, where they leak out. This behavior is very sensitive to temperature, pressure, material composition, and surface finish. Lower external pressure increases the outgassing rate of materials in vacuum conditions. Moisture absorption also causes mass loss during testing. Knowledge about the factors aids in forecasting material behavior under the actual conditions of operation.

Key Parameters Measured During Outgassing Testing

Outgassing tests focus on measurable parameters. The total mass loss (TML) measures the total amount of volatiles lost during exposure. Technicians determine the percentage of condensable material on colder surfaces by collecting volatile condensates, which directly indicates the risk of contamination. Engineers use Water Vapor Regain (WVR) to assess a material’s ability to reabsorb water after testing. Analysts maintain tight control over test temperatures, exposure times, and vacuum levels to guarantee consistency and reproducibility. Collected Volatile Condensable Material (CVCM) is another critical metric being determined during the outgassing test. CVCM evaluates how much of a material’s outgassed substance vaporizes and condenses onto nearby surfaces

Outgassing is performed using two methods described below.

What Are the ASTM Standards to Follow for Outgassing Testing?

The standard test methods used for outgassing testing are ASTM E595 and ASTM E1559. The details are given below.

ASTM E595 

It is recommended to qualify materials for aerospace, space, and other vacuum-related applications. Analysts measure Total Mass Loss (TML), Collected Volatile Condensable Material (CVCM), and Water Vapor Regained (WVR) under standard test conditions. This standard facilitates material acceptance testing, helps ensure compliance with aerospace contamination limits, and allows engineers to compare candidate materials using defined pass/fail criteria.

ASTM E1559 

It is recommended when detailed knowledge of outgassing characteristics is needed. This method measures dynamic outgassing rates and identifies volatile species in materials as they heat under high vacuum. Researchers recommend this standard for contamination-sensitive optical systems, semiconductor equipment, advanced vacuum technologies, and projects requiring thorough outgassing investigations.

Significance of the Outgassing Testing

Engineers use outgassing testing to evaluate material behavior for applications in vacuum, aerospace, and contamination-sensitive semiconductor environments. Vapors escape from objects and condense on nearby surfaces, which causes optical degradation, electrical failure, decreased thermal efficiency, or contamination of precision equipment. Beyond measuring mass loss, engineers use tests for condensable residues and moisture regain to compare materials, verify compliance with industry requirements, mitigate contamination risks, and enhance long-term product reliability. Manufacturers also use these tests to qualify materials, ensure quality assurance, and select materials during product development.

Applications

Some common applications are satellite and spacecraft parts, optical instruments, semiconductor manufacturing equipment, vacuum systems, medical devices, and high-performance electronics. Commonly used for adhesives, sealants, polymers, elastomers, coatings, composites, lubricants, thermal interface materials, cable insulation, and printed circuit board materials. Engineers often qualify and accept materials in accordance with ASTM E595. Researchers prefer ASTM E1559 for detailed characterization of outgassing rate and contamination behavior in advanced research and precision engineering applications.