Perme­a­bil­ity Cups

The perme­a­bil­ity of a coat­ing to water vapor is mea­sured by sus­pend­ing a free film of the mate­rial across the top of a wide shal­low cup. Then, in a con­trolled envi­ron­ment, a des­ic­cant is used to draw water vapor through the film into or out of the cup. Weight loss or gain of the cup’s con­tent over a spe­c­i­fied period is used to deter­mine the rate of vapor trans­mis­sion through the film. The perme­a­bil­ity of a film to many other sub­s­trates in the gaseous state can be tested in a sim­i­lar fashion.

Perme­a­bil­ity Cup

The BYK-Gard­ner Perme­a­bil­ity Cup is a shal­low cylin­der with a threaded flange, flat retain­ing washer and threaded ring cover. Rub­ber gas­kets are used to tightly seal the spec­i­men between the cup and the ring cover. The cup and cover are knurled for easier han­dling.
Two dif­fer­ent size cups are avai­l­able:

• Large 25 cm² cup meets the ASTM stan­dard
• Small 10 cm² cup allows the use of a smaller spec­i­men and less des­ic­cant

Pro­ce­dure
Dur­ing a test, vapor passes from the cup through the film spec­i­men to an open con­tainer of des­ic­cant or other absor­bent mate­rial in a con­trolled envi­ron­ment. The perme­a­bil­ity cup and other con­tainer are sealed together in a larger con­tainer to pro­vide con­trol of the vapor pres­sure.

Test­ing may also be set up to allow pas­sage of vapor from a solu­tion in the open con­tainer through the test film to a des­ic­cant or other absor­bent mate­rial within the perme­a­bil­ity cup.