 The diameter of the powder used is relative to the density (g/m²) of the stock (paper or board) being printed.For 150 g/m² paper the ideal anti-set-off spray powder would be 15 µm in diameter, for 200 g/m² 20 µm, through to 70 µm for heavy board (700 g/m²).Most manufactures of spray powder offer both coated and uncoated powders.