The ISO 3251 "Determination of non-volatile matter content in Paints, varnishes and plastics" standard specifies a method for the determination of non-volatile matter content in Paints, varnishes and plastics. The content of the remaining non-volatile matter is calculated by heating the sample to a specified temperature, after removing the volatile components, and measuring the mass of the remaining non-volatile matter. This method is suitable for quality control, formulation optimization and product performance evaluation of various Coatings and plastics. The standard details the test equipment, sample preparation, heating conditions and calculation methods to ensure the accuracy and conformity of the test results. Implementing this standard helps manufacturers control product mass and ensure the Stability and durability of coatings and plastics in practical applications.