As Large Scale Integration (LSI) Devices become more advanced, feature sizes are continuing to get smaller and the associated film thicknesses deposited are reaching atomic levels. As a result, the outgassing and permeation characteristics of elastomeric seal materials used in high temperature and high vacuum processes are important factors that can influence film uniformity, quality and consistency. DuPont Performance Polymers (DPP) has developed a practical test methodology for comparing relative permeability characteristics of O-ring seals under high vacuum conditions using a Quadrupole Mass Analyzer (QMA) and Ionization Vacuum Gauges. The method will be discussed and a sampling of data generated for various O-ring materials / compositions will be reviewed.