If you've ever handled a polymerized epoxy compound you would be fairly confident that the material you were holding was a 100% soid substance. However, even completely cured polymer products can contain volatile compounds trapped within the polymer structure.
Over time these volatile compounds may escape as a gas and condense on nearby sensitive equipment, potentially obscuring them. This process is formally known as outgassing and NASA has developed a specialized test to determine if a material outgasses to an extent that it may compromise spacecraft equipment.
The material is exposed to 50% relative humidity at 25C for 24 hours and then weighed.
The material is then placed in a heated vacuum chamber and exposed to 125C (257F) and at minimum 5x10-5 torr for another 24 hours. Any volatiles that may outgas during this process are able to escape through a port hole in the vacuum chamber and condensate on a cooled plate.
The material is then weighed to determined Total Mass Lost (TML) and the condensate is weighed to determine Collected Volatile Condensable Materials (CVCM).
OPTIONAL: The material is then again exposured to 50% relative humidity for 24 hours and weighed again to determine Water Vapor Regained (WVR).
Analyzing The Results
With these three values (TML, CVCM and WVR) we can determine whether the material has passed or failed (basically whether or not the material is fit for use with spacecraft equipment).
If CVCM <0.1% and TML < 1%, the material passes.
If CVCM <0.1% and TML > 1 %, the material can pass if the TML-WV <1%.
If CVCM > 0.1% or TML-WVR > 1%, the material fails.
Although NASA outgassing requirements were originally designed to qualify materials for spacecraft equipment, outgassing results apply to many more applications than space travel. Anytime a polymer material is exposed to an extreme environment (severe vacuum, high temperature, etc.) outgassing potential is increased. For electronic and display applications that may be exposed such extremes, choosing a NASA low outgassing polymer is a smart decision.