Cobb (Paper Water Absorption)
Compute the Cobb value of a paper, Cobb = mass gain (g) / area (m²), in g/m², the amount of water absorbed by one face of the paper in a standardized time (usually 60 s). It measures resistance to water penetration, crucial in packaging papers, printing (glue/ink control) and products that contact liquids. A low Cobb indicates good sizing. Enter the mass gain and the tested area.
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Cobb value (paper water absorption)
How much water does a sheet of paper take up? The Cobb test answers that in a standardised way: a column of water is held against one face of the sheet for a set time (usually 60 seconds — hence 'Cobb60'), and the mass gain per unit area is measured: Cobb = mass gain (g) / area (m²), in g/m². It measures resistance to water penetration through one face — a vital property in many grades. In packaging (corrugated boxes, cement sacks, disposable cups, food wrappers), a low Cobb value is essential so the paper will not wet through, soften and lose strength on contact with moisture or liquids. In printing, the Cobb value governs how ink (water-based, in flexography) and adhesive penetrate the sheet — affecting print definition, drying and curl. Cobb is controlled by sizing: hydrophobic agents (AKD and ASA resins, rosin size) are added to the stock or to the surface to repel water. Unsized papers such as blotting and filter paper have a very high Cobb value (they soak avidly, by design); papers meant to hold liquids have a very low one. Cobb tests are run at several contact times (60 s, 1800 s) according to the application. Enter the water mass gain and the area tested.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.