Gelbo Flex Testing

Intertek provides Gelbo-Flex testing of flexible barrier materials like packaging and film.

One key property of flexible barrier material is the resistance against repetitive strain, which is called flex durability, or Gelboflex. Intertek operates specialized Gelbo-flex equipment to determine the flex resistance, also called the flex tester. The sample size (200 by 280 mm) is attached to the flex tester mandrels. The flexing action consists of a twisting motion combined with a horizontal motion (compression), thus repeatedly twisting and crushing the film. The test set up gives a twisting motion of 440º in the first 90 mm of the stroke and is followed by a straight horizontal motion of 65 mm. The speed is 45 cycles per minute.

After a predetermined number of strokes the material is examined. In general the formation of pinholes is determined by use of colored turpentine and allowing it to stain through the pinholes onto a white backing. The number of pinholes is a measure for the flexing resistance of the material.  Other evaluation methods such as gas permeation are also available (Oxygen Transmission Rate)

The flex testing method method used is ASTM F392, "Flex durability of flexible barrier materials".