The STD 478 water vapour absorption test apparatus measures a material's affinity to absorb water vapour.
A test specimen is clamped between the open end of a test pot (containing a specified volume of water) and an impermeable seal. The pot is then stored at a specified temperature for a set time, after which the change in mass of the specimen is determined.
The STD 478 test apparatus consists of six test pots each having an internal diameter of 35mm and a volume of 100cm3, a removable lid which can be securely clamped over the open end of the pot and an impermeable seal held over the end of the pot by the lid.
In addition to the STD 478 apparatus, a laboratory balance and a stopwatch are necessary to determine water vapour absorption (available from SATRA).