ASTM F392 Gelbo Flex Test

Standard Test Method for Flex Durability of Flexible Barrier Materials

The GF-392 Gelbo Flex Tester is a specialised test machine primarily designed for flex durability testing of flexible barrier materials, e.g. plastic films, laminates, foils, and coated paper. The machine conforms to ASTM F392 and some other internationally recognised test standards.

The flex resistance of materials is determined after flex durability testing, by identifying pinhole formation or measuring other properties such as gas permeation rates. This is important to determine the resistance of different materials to flex formed pinholes and breakdown of barrier layers.

The Gelbo Flex Tester comprises two mandrels of 90mm diameter, one fixed and the other twisting and moving horizontally via a drive shaft, guide bearing and motor. The mandrels are set in a home position 180mm apart, and the test material is attached with clips to form a tube.

The moving mandrel provides a twisting action followed by a horizontal motion, which repeatedly twists and crushes the test material. The drive mechanism has two settings for long and short strokes.

The machine is controlled via an HMI keypad, by selecting the number of cycles required according to the test method/standard used. This is in the range of 2,700 cycles to 20 cycles at a constant rate of 45 cycles per minute.

On completion, the test material can be checked for pinholes by painting on a turpentine solution and identifying any marking onto a white sheet of paper, or by gas transmission rate testing.

For multi-layer structured materials, individual layers may have failures in integrity which do not present as complete pinholes, in such cases gas transmission rate testing may be useful as a measurement.


  • Gelbo Flex Tester

    Gelbo Flex Tester designed to measure flexible barrier materials for flex durability to ASTM F392