Opacity

Opacity is a measure of the ability of paper to obstruct the passage of light through the sheet, and is run according to TAPPI Test Method T425. Paper opacity determines whether text or graphics are visible from the opposite side of the paper.  Opacity is influenced by basis weight and filler or coating materials that are added to the sheet.  Percent opacity is the ratio of the reflectance of a single paper sheet backed with a black backing to the reflectance of the same sheet backed with a white backing.  If the white backing is a stack of the same paper, the opacity value is referred to as printing opacity.  If the white backing is a surface with a 0.89 reflectance, the opacity value is referred to as contrast ratio.

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