This International Standard specifies two procedures for the preparation of laboratory sheets prior to measuring the diffuse blue reflectance factor (ISO brightness). One is the traditional procedure based on preparation of sheets in a Büchner funnel using a filter paper or a wire screen. In the other procedure, the sheets are prepared in a standard sheet former (conventional or Rapid Köthen). Details of the subsequent measurement procedure are given in ISO 2470. It is applicable to all wood pulps and to most other types of pulp. Pulps with very long fibres, such as those made from unshortened cotton, flax and similar materials, shall be reduced to a suitable fibre length before testing by this method. This International Standard shall be used in conjunction with ISO 2469 and ISO 2470.