The ISO 2471:2008 standard specifies a method for the determination of paper and Cardboard opacity (paper backing), which is tested using the diffuse reflection method. This method is suitable for white and nearly white paper and Cardboard, including paper treated with fluorescent whitening agents. The opacity value is calculated by measuring the intensity of light reflected by paper at a specific Light source to evaluate the ability of paper to block rays of light. This standard provides a uniform opacity test method for the paper industry and is widely used in paper quality control and printability assessment.