Water absorptiveness is a function of various characteristics of paper and board like porosity, sizing etc. Cobb test method is applicable to sized paper, paperboard and corrugated fibreboard. In water absorptiveness also known as cobb test, the mass of water absorbed in a particular time by 1 square meter of paper, board or corrugated fibreboard under 1 cm of water.

The Cobb sizing tester allows one side sample to be wetted uniformly with the beginning of the soaking period. Removal of water from the sample takes place at the end. The sample holder has a metal ring with a machines lower face i.e. 4.44 in. inside diameter and 2.5 cm high and about 0.6 cm thick, clamped to a flat base plate of the same or bigger size. It has a rubber mat at the base plate, larger than outside dimensions of the ring on which the sample is tightened.

The Cobb test determines the amount of water absorbed into the surface by a sized paper, corrugated fibreboard paper etc. in a set period of time usually 60 or 180 seconds. Water absorbency can be denoted by g/m2. The water absorbency of a material affects the printability and set rate of water based adhesives.

Cobb sizing tester is an equipment that measures the water absorptive quality of packaging materials and resists the damage caused to the products.

Method for Cobb testing:

  • Take a sample cut in circular shape greater than the diameter of the rubber. Weigh the sample.
  • Place the sample between the cylinder and rubber pad. Clamp the sample manually using a screw.
  • The sample should not crush while clamping and then overturn the cylinder back to its position.
  • After clamping the sample, add 100 ml or 250 ml of water up to the marking in the cylinder. Start the stop water for 1 to 10 minutes for single to multi-layered board.
  • Remove water from the cylinder when the test completes and takes out the sample. Remove the excessive amount of water using hand roller.
  • The test is completed after weighing of sample again.
  • The Cobb value is determined by subtracting the weight of the sample taken before testing from the weight of the sample after testing.

The Cobb test is important because it tests the ability of paper to prevent the entry of water. The Cobb tester is manufactured according to international standards as IS 1060, TAPPI-T441. It is built with corrosion resistant body and stainless steel test area available in an effective price for quality tests.