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Water Cobb is a test of surface and internal sizing. It can be run from either the back side or the coated side of the paper. Each test evaluates a different property of the paper. The test run from the back side measures the base sheet sizing. The test run from the coated side responds to the "openness" of the coating. This method is less frequently used. A column of water is placed on the paper for 2 minutes, and the amount of water absorbed is measured. More water resistance will result in a lower Water Cobb.