ISO 535 Cobb Method Testing

ISO 535 Package Testing: Water Absorptiveness Testing – Cobb Method

ISO 535 package testing determines the water absorptiveness of paper and board. As an ISTA and ISO 17025 certified lab, we realize the importance of ISO 535 testing. Meeting the ISO 535 water absorptiveness testing requirements can be difficult. We understand the challenges and guide companies through the process.

Keystone Package Testing partners with customers to achieve package compliance. Our accurate test reports are delivered quickly. We create an accurate test plan to eliminate expensive over-testing. Keystone takes a consultative approach throughout the entire test program.

Request a quote to receive testing services customized to your specific needs. Contact us to receive more information on ISO 535 standard conditioning test.

Summary of Paper and Board Water Absorptiveness – Cobb Method

The purpose of the ISO 535 method is to determine the water absorptiveness of sized paper and board. This Cobb testing method also includes corrugated fibreboard under standard conditions. It may not be suitable for paper of grammage less than 50 g/㎡ or embossed paper.

Water Absorptiveness (Cobb Value): The calculated mass of water absorbed in a specified time by 1 m2 of paper or board under specified conditions.

A test piece is weighed immediately before and immediately after exposure for a specified time of one surface to the water, followed by blotting. The result shows an increased mass expressed in grams per square meter.

Note that the standard gives a general indication for use with aqueous solutions. However, this method is not intended to be used for precise evaluation of the writing properties of paper.

ISO 535 Package Testing Procedures


The conditioning of test specimens is carried out in accordance to ISO 187.

At least 10 test pieces of sufficient size are cut from the specimen. It must be ensured that the test area is avoided by contact with hands. Furthermore, the area must be free from visible folds, creases, cracks, or other defects. If watermarks are present, these areas are avoided as well.


Both surfaces that come into contact with the test piece are dried before commencing each test. The test pieces are weighed to the nearest milligram. Then, they are placed to be tested with the uppermost surface on the base plate.

Test duration lasts between when the water first makes contact with the test piece until the start of the blotting. Furthermore, for the purpose of this standard, the times of the test may be increased according to water absorptiveness and to the special nature of the specimen under consideration.

Test plates will be rejected if they have been penetrated by the water. They will also be rejected if they show signs of leakage or show excess water after blotting. If no reduced time is fitting, this ISO 535 method is not suitable.

When mounting the test piece, the upper edge of the surface which will come into contact with the test piece is dried before the start of each test. The cylinder is placed with the machine edge in contact with the test piece and clamped firmly to prevent any leakage of water between it and the test piece.

Test Report

After the completion of the Cobb Method, a test report will consist of general and in-depth information. Information includes:

  • Date, time, location, and specific test engineer
  • Reference to the ISO 535 standard
  • Conditioning atmosphere used
  • Any circumstances or factors that may be affected or influenced by the results

Significance of ISO 535 Integrity Testing

By measuring the ability of these materials to absorb water, the ISO 535 Cobb method testing helps ensure the durability, printability, and overall quality of paper-based products. This essay will delve into the significance of ISO 535 Cobb method testing, highlighting its importance in various industries.

Additionally, packaging materials, such as cardboard and paperboard, are often subjected to moisture during transportation and storage. ISO 535 Cobb method testing helps evaluate the water resistance capabilities of these materials.

Lastly, ISO 535 Cobb method testing also serves as a valuable tool in the research and development of paper and board materials. The Cobb Method enables scientists and engineers to assess the impact of various factors, such as material composition, surface treatments, and manufacturing processes, on water absorbency.

Expert ISO 535 Paper and Board Package Laboratory Testing

Keystone can accommodate flexible and rigid packages of all sizes, including large pallets. We have a full lab of test equipment which permits us to provide short lead times on scheduling. In addition to ISO 535 testing, Keystone also has a full scope of expertise including sterile barrier, cold chain, and inclined impact.

Are you ready to get started? We are. Contact us and learn first hand why so many companies partner with Keystone to achieve their paper, board, and related product certification needs.


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