"Opacity" is a fundamental optical property of paper, which is a measure of the amount of light that can pass through or be absorbed by the paper. The greater the opacity value of the paper, the less light it transmits or allows to pass through, and vice versa. Opacity is a very important property to consider when printing on various papers such as duplex, stationery, tracer, etc. The opacity of paper is affected by many factors and components, such as paper thickness/grammage, quality and amount of fillers, degree of bleaching of fibers, coating, beating, pressing, calendering, supercalendering, etc. Papermaking process. It is measured as the percentage of light that is absorbed or reflected (diffuse). A piece of paper, and this measurement is done using an "Opacimeter". There are two measurement methods, one is the "contrast method" and the other is the "diffuse opacity method". The standard test methods followed are TAPPI T425 and ISO 2471.
