The ISO 699 standard specifies a method for determining the alkali resistance of pulp. The method uses a sodiumhydrate solution at a fixed concentration, commonly used concentrations of 18%, 10% and 5% (mass fraction), to determine the amount of alkali-insoluble components in pulp. This method is suitable for various types of pulp, including chemical pulp and mechanical pulp. The alkali resistance of pulp is assessed by determining its solubility under alkaline conditions. The standard is widely used in the paper industry for pulp quality control and process optimization.