GB/T 3671.2-2025 "Determination of Cold Water Solubility of Water-Soluble Dyes" replaces the 1996 edition. It adopts the redrafting method to modify and adopt the international standard, specifying the method for determining the cold water solubility of water-soluble dyes. The standard introduces new terms and definitions, optimizes technical requirements such as filter paper specifications, vacuum adjustment, and filtration procedures, and explicitly sets 25°C as the test temperature. The solubility limit is determined by preparing solutions of varying concentrations, performing vacuum filtration, visually evaluating residues, and measuring filtration time. It is applicable to the performance testing of relevant dyes, providing a unified technical basis for dye production, application, and quality control, thereby ensuring the accuracy and comparability of test results.