The ISO 7686:2005 "Determination of opacity for plastic pipes and fittings" standard specifies the test method for evaluating the opacity of plastic pipes and fittings. Opacity is an important characteristic of plastic piping systems that directly affects their performance in light environments. The standard details the test equipment, sample preparation, test procedures and calculation methods for results to ensure the repeatability of the test process and the reliability of the results. The method is suitable for a variety of plastic pipes and fittings, helping manufacturers and users to evaluate the mass of the product and ensure that it meets the relevant application requirements. It provides a scientific basis for product development, quality control and trade inspection.