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Short answer. ASTM E595 is the standard test method for total mass loss (TML) and collected volatile condensable materials (CVCM) from outgassing in a vacuum. A small sample is held at 125 °C in vacuum for 24 hours, and the method reports how much mass it lost and how much condensed on a 25 °C collector. NASA’s database adds an optional third figure, water vapor regained (WVR).
Definition and scope
The full title of ASTM E595, as NASA’s Goddard Space Flight Center quotes it, is “Total Mass Loss (TML) and Collected Volatile Condensable Materials (CVCM) from Outgassing in a Vacuum Environment.” It is a screening test for materials that will sit in vacuum, where released vapors can condense on nearby surfaces. NASA states the purpose of its outgassing database as supplying data to “substantiate low outgassing performance to verify the suitability of a material for spaceflight environments.”
Two points of scope matter for anyone reading a datasheet. First, the figures come from one fixed set of conditions (below), so they compare materials with each other; they are not a prediction of how much a material releases at another temperature or pressure. Second, the NASA database does not publish pass/fail limits, so a number on its own is not a certificate. Whoever is selecting the material sets the criteria.
How the test is run
The NASA Goddard Outgassing Database user guide describes the E595 setup in enough detail to see why the two headline numbers differ. Each parameter below comes from that guide.
| Parameter | Value described by NASA |
|---|---|
| Sample size | 100 to 300 mg, nominally 250 mg, in a pre-weighed aluminum foil boat |
| Pre-conditioning | 24 hours at 25 °C, 50% relative humidity, standard atmospheric pressure |
| Heated source | Copper bar at 398 K (125 °C) for 24 hours in vacuum |
| Collector | Held at 298 K (25 °C), 12.7 mm (0.5 in.) from a 6.3 mm (0.25 in.) exit port |
| Tapes and film adhesives | Tested on pre-weighed aluminum foil |
The geometry explains the result. Everything the sample loses counts toward TML, whether or not it lands anywhere. Only vapor that leaves through the port and condenses on the cooler collector counts toward CVCM, so a material can lose mass without depositing much.
TML, CVCM and WVR: what each figure means
| Figure | How NASA defines it |
|---|---|
| TML (total mass loss) | Calculated from the sample weight before and after the 125 °C exposure, as a percent of the starting mass |
| CVCM (collected volatile condensable material) | Weight of a clean collector compared with the collector carrying condensate, as a percent of the starting sample mass |
| WVR (water vapor regained) | Water readsorbed over 24 hours at 25 °C, as a percent of the starting mass; optional under E595 |
WVR is recorded separately from TML and CVCM, so a reader can see how much water a material took back after the test rather than folding it into the loss figures.
Where it matters for labs, clinics and supply decisions
Most staff meet E595 as a line on a material or component specification, or as a search in the NASA database. The database lets you filter by material, application category and numeric ranges for TML, CVCM and WVR. A short checklist, taken from the user guide, for reading an entry:
- Check the cure. Cure conditions are recorded with each entry. NASA states that “If no cure is listed, the cure data are not known,” so an entry without one does not describe a specific cured state.
- Check the age of the data. The guide notes the data span about 25 years and that “It is likely that some materials have changed over this time span.”
- Use batch testing for critical applications. NASA says batch testing “should be the prudent course” where the application is critical, and describes the data as a guide to selection with “a fair degree of confidence,” not a substitute for testing.
- Apply your own limits. The original screening criteria were a maximum TML of 1.0 percent and a maximum CVCM of 0.10 percent, and the database’s published listing included only materials meeting both. The database search itself sets no limit.
A related 1993 NASA Goddard report, Campbell and Scialdone’s “Outgassing Data for Selecting Spacecraft Materials,” confirms the same test basis: its data derive from tests at 398 K (125 °C) for 24 hours in vacuum per ASTM E-595-90, grouped by likely use. Where a purchaser’s own quality system covers incoming materials, an SOP and the consensus-standard references it cites are the place to record which edition and which limits apply. Equipment that holds samples under vacuum is a separate question from material outgassing, and sits with IQ/OQ/PQ qualification and the equipment lifecycle.
Common misunderstandings
“A material that passed E595 is certified low-outgassing for any use.”
The test fixes one temperature (125 °C), one duration (24 hours) and a defined collector temperature (25 °C). The numbers compare materials under those conditions. NASA’s own guidance pairs them with batch testing for critical use.
“The database tells me whether a material passes.”
It does not. The database reports measured TML, CVCM and WVR and lets you filter by range; the limits are your choice. The 1.0 percent and 0.10 percent figures are the historical criteria, not a universal pass line.
“An entry from the database describes today’s product.”
Not necessarily. Entries can be decades old, and a material with no recorded cure is described as unknown rather than assumed cured. Formulations may have changed since the test.
“CVCM and TML measure the same thing.”
TML is everything lost from the sample. CVCM is only what condensed on the collector, as a share of the starting sample mass. The condensate is a subset of what was lost, so CVCM cannot exceed the mass that left the sample.
FAQ
What does ASTM E595 measure?
Total mass loss and collected volatile condensable materials from a sample held in vacuum at 125 °C for 24 hours, with an optional water vapor regained figure.
What are the original E595 screening criteria?
The original criteria cited by NASA were a maximum TML of 1.0 percent and a maximum CVCM of 0.10 percent.
Where can I look up E595 results for a material?
The NASA Goddard Outgassing Database reports TML, CVCM and WVR and is searchable by material and application category.
Does a database entry replace testing my own batch?
No. NASA describes the data as a selection guide and recommends batch testing where the application is critical.
Sources
- NASA Goddard Space Flight Center, Outgassing Database User Guide, checked 29 October 2026.
- NASA Goddard Space Flight Center, Outgassing Database, checked 29 October 2026.
- Campbell and Scialdone, Outgassing Data for Selecting Spacecraft Materials, NASA Technical Reports Server (1 September 1993), checked 29 October 2026.
