Perm Cup - Water Vapor Permeability

Perm cups are used to determine the permeability of films to the vapor of water and other liquids. Materials that are tested include paint, varnish, thin plastic films and other types of sheets thin enough to be tightly sealed in place across the face of the cup. Permeability is expressed as the weight of a vaporous material that passes through a specified area and thickness of free film within a specified time interval under controlled conditions.

• The face opening of the cup is 25 square centimeters.
• The volume of the cup is 25 milliliters.
• Normal test weight of the cup assembly is less than 140 grams.
• All cup surfaces are protected by an alodine coating.
• Thick gaskets and test samples are now accommodated by eliminating interference between the cap and cup ring restraining pins.

Either a test liquid or a desiccant is placed in the cup, depending on the specified conditions of the test. A sample of the test material, precut to the outside dimensions of the clamp ring, is placed on the top surface of the cup, using gaskets if required, and sealed against the cup surface by tightening the cap ( for specimen preparation see ASTM D-823 & D- 4708).

The assembly is then accurately weighed and placed in a specified controlled atmosphere. Periodic weighing determines weight loss or gain from which rate of vapor transmission is calculated. Small 10 cm² cup allows the use of a smaller specimen and less desiccant. Approximate weight 88g w/o gaskets.

Clamp ring detail pictured left.