Material that is a nonporous, flexible film can be used for gelbo flex testing. Typically, this is a clear plastic film that you would see on the on the reverse side of Tyvek pouch or foil material for a foil-to-foil pouch.
The first step is to cut a swatch of film that is about the size of 1 piece of printer paper. Then, the swatch is mounted on the gelbo flex tester by curling the swatch around the two round mandrels.
When we start the gelbo flex tester, one of those mandrels will twist and compress together and then open back up and untwist. This is done repeatedly to simulate the flexing that materials endure during transit testing.
After the film swatch has been stressed, we fix it to a white paper backing. Once the swatch is secured, we essentially paint it with the blue dye we use for seal integrity testing by dye leak ASTM F1929. If there are any pinholes or flex cracks, the toluidine blue dye will leak through and stain the white paper backing. From there we can observe the crack patterns.
Some variables we might control are number of cycles we expose the materials to. This could range from 250–1000 cycles.