This document specifies an oven-drying method for the determination of the dry matter content in suspensions of cellulosic nanomaterials. The procedure is applicable to cellulosic nanomaterial suspensions which do not contain any appreciable quantities of materials other than water that are volatile at the temperature of 105 °C ± 2 °C. It is used, for example, in the case of cellulosic nanomaterial suspensions samples taken for chemical and physical tests in the laboratory, when a concurrent determination of dry matter content is required. NOTE 1:  ISO 638-1[1] specifies the dry matter content in paper, board, pulp and cellulosic nanomaterials in solid form, which all can be produced from virgin and/or recycled materials; ISO 287[2] specifies the determination of moisture content of a lot of paper and board; ISO 4119[3] specifies the determination of stock concentration of aqueous pulp suspensions; ISO 801 (all parts)[4] specifies the determination of saleable mass in lots. NOTE 2:  This document determines the total dry matter content of the sample, including any dissolved solids. If only the cellulosic material content free of dissolved solids is desired, dissolved solids are removed prior to measuring the dry matter content e.g. by washing or dialysis, taking care to retain all cellulosic material.